Method and apparatus for image encoding, and method and apparatus for image decoding

ABSTRACT

Provided is an image decoding method including determining a plurality of coding units in a chroma image by hierarchically splitting the chroma image, based on a split shape mode of blocks in the chroma image of a current image, and decoding the current image, based on the plurality of coding units in the chroma image. In this regard, the determining of the plurality of coding units in the chroma image may include, when a size or an area of a chroma block from among a plurality of chroma blocks to be generated by splitting a current chroma block in the chroma image is equal to or smaller than a preset size or a preset area, not allowing splitting of the current chroma block based on a split shape mode of the current chroma block, and determining at least one coding unit included in the current chroma block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 17/053,571, filed on Nov. 6, 2020, which is aNational Stage Entry Application of International Application No.PCT/KR2019/005673, filed on May 10, 2019, which claims priority to U.S.Provisional Patent Application No. 62/683,255, filed on Jun. 11, 2018,and U.S. Provisional Patent Application No. 62/669,667, filed on May 10,2018, in the U.S. Patent and Trademark Office, the disclosures of whichare incorporated by reference herein in their entireties.

TECHNICAL FIELD

A method and apparatus according to an embodiment may encode or decodean image by using various-shape coding units included in the image. Amethod and apparatus according to an embodiment may determine at leastone coding unit by hierarchically splitting a chroma image, and mayencode or decode the chroma image by using the at least one coding unit.

BACKGROUND ART

As hardware capable of reproducing and storing high-resolution orhigh-quality image content has been developed and become widely popular,a codec capable of efficiently encoding or decoding the high-resolutionor high-quality image content is in high demand. The encoded imagecontent may be reproduced by decoding it. Recently, methods ofeffectively compressing high-resolution or high-quality image contentare used. For example, an efficient image compression method isimplemented through a process of randomly processing an image to beencoded.

Various data units may be used to compress images, and an inclusionrelation may exist between the data units. A data unit may be split byusing various methods to determine a size of the data unit to be used inimage compression, and then an optimal data unit may be determined basedon a characteristic of an image, such that the image may be encoded ordecoded.

DESCRIPTION OF EMBODIMENTS Solution to Problem

According to an embodiment of the disclosure, an image decoding methodincludes: determining a plurality of coding units in a luma image byhierarchically splitting the luma image, based on a split shape mode ofblocks included in the luma image of a current image; determining aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks in the chromaimage of the current image; and decoding the current image, based on thedetermined plurality of coding units in the luma image and thedetermined plurality of coding units in the chroma image, and whereinthe split shape mode is a mode based on at least one of a splitdirection and a split type of a block, and wherein the determining ofthe plurality of coding units in the chroma image includes, when a sizeor an area of a chroma block from among a plurality of chroma blocks tobe generated by splitting a current chroma block in the chroma image isequal to or smaller than a preset size or a preset area, not allowingsplitting of the current chroma block based on a split shape mode of thecurrent chroma block, and determining at least one coding unit includedin the current chroma block.

According to an embodiment of the disclosure, an image decodingapparatus includes: at least one processor configured to determine aplurality of coding units in a luma image by hierarchically splittingthe luma image, based on a split shape mode of blocks included in theluma image of a current image, determine a plurality of coding units ina chroma image by hierarchically splitting the chroma image, based on asplit shape mode of blocks in the chroma image of the current image, anddecode the current image, based on the determined plurality of codingunits in the luma image and the determined plurality of coding units inthe chroma image, and wherein the split shape mode is a mode based on atleast one of a split direction and a split type of a block, and when theat least one processor determines the plurality of coding units in thechroma image, and when a size or an area of a chroma block from among aplurality of chroma blocks to be generated by splitting a current chromablock in the chroma image is equal to or smaller than a preset size or apreset area, the at least one processor is configured to not allowsplitting of the current chroma block based on a split shape mode of thecurrent chroma block, and determine at least one coding unit included inthe current chroma block.

According to an embodiment of the disclosure, an image encoding methodincludes: determining a plurality of coding units in a luma image byhierarchically splitting the luma image, based on a split shape mode ofblocks included in the luma image of a current image; determining aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks included in thechroma image of the current image; and encoding the current image, basedon the determined plurality of coding units in the luma image and thedetermined plurality of coding units in the chroma image, and

wherein the split shape mode is a mode based on at least one of a splitdirection and a split type of a block, and

wherein the determining of the plurality of coding units in the chromaimage includes,

when a size or an area of a chroma block from among a plurality ofchroma blocks to be generated by splitting a current chroma block in thechroma image is equal to or smaller than a preset size or a preset area,not allowing splitting of the current chroma block based on a splitshape mode of the current chroma block, and determining at least onecoding unit included in the current chroma block.

A computer program of an image encoding method or an image decodingmethod according to an embodiment of the disclosure may be recorded on acomputer-readable recording medium.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram of an image decoding apparatus, according tovarious embodiments.

FIG. 1B is a flowchart of an image decoding method, according to variousembodiments.

FIG. 1C is a block diagram of an image decoder according to variousembodiments.

FIG. 2A is a block diagram of an image encoding apparatus, according tovarious embodiments.

FIG. 2B illustrates a flowchart of an image encoding method according tovarious embodiments.

FIG. 2C is a block diagram of an image encoder according to variousembodiments.

FIG. 3 illustrates a process, performed by the image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

FIG. 4 illustrates a process, performed by the image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

FIG. 5 illustrates a process, performed by the image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

FIG. 6 illustrates a method, performed by the image decoding apparatus,of determining a preset coding unit from among an odd number of codingunits, according to an embodiment.

FIG. 7 illustrates an order of processing a plurality of coding unitswhen the image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

FIG. 8 illustrates a process, performed by the image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apreset order, according to an embodiment.

FIG. 9 illustrates a process, performed by the image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined as the image decoding apparatus splits afirst coding unit, satisfies a preset condition, according to anembodiment.

FIG. 11 illustrates a process, performed by the image decodingapparatus, of splitting a square coding unit when split shape modeinformation indicates that the square coding unit is to not be splitinto four square coding units, according to an embodiment.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

FIG. 16 illustrates a processing block serving as a criterion fordetermining a determination order of reference coding units included ina picture, according to an embodiment.

FIGS. 17A and 17B are diagrams for describing a method by whichsplitting to chroma blocks whose size is equal to or smaller than apreset size is not allowed when a splitting tree type indicates a singletree, according to various embodiments.

FIG. 18 is a diagram for describing a method by which splitting of achroma block whose size is equal to or smaller than a preset size is notallowed when a splitting tree type indicates a dual tree, according toan embodiment.

FIG. 19 is a diagram for describing a method of splitting a block, whichis located at a boundary of a picture, by using a split shape mode basedon a direction of the boundary, according to an embodiment.

FIGS. 20A and 20B are diagrams for describing a method of splitting ablock at a picture boundary according to whether a minimum size of ablock is obtainable when the block at the picture boundary is binarysplit by applying an allowed binary split depth thereto, according to anembodiment.

BEST MODE

According to an embodiment of the disclosure, an image decoding methodincludes: determining a plurality of coding units in a luma image byhierarchically splitting the luma image, based on a split shape mode ofblocks included in the luma image of a current image; determining aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks in the chromaimage of the current image; and decoding the current image, based on thedetermined plurality of coding units in the luma image and thedetermined plurality of coding units in the chroma image, and whereinthe split shape mode is a mode based on at least one of a splitdirection and a split type of a block, and

wherein the determining of the plurality of coding units in the chromaimage includes,

when a size or an area of a chroma block from among a plurality ofchroma blocks to be generated by splitting a current chroma block in thechroma image is equal to or smaller than a preset size or a preset area,not allowing splitting of the current chroma block based on a splitshape mode of the current chroma block, and determining at least onecoding unit included in the current chroma block.

The split type may indicate one of binary split, tri split, and quadsplit.

The preset size may be one of 4×2, 2×4, and 2×2.

The preset area may be one of 8 and 4.

When the size or the area of the chroma block from among the pluralityof chroma blocks to be generated by splitting the current chroma blockin the chroma image is equal to or smaller than the preset size or thepreset area, the not allowing of the splitting of the current chromablock based on the split shape mode of the current chroma block, and thedetermining of the at least one coding unit included in the currentchroma block may include: determining whether the size or the area ofthe chroma block from among the plurality of chroma blocks to begenerated by splitting the current chroma block in the chroma image isequal to or smaller than the preset size or the preset area, accordingto whether a condition based on a size or an area of the current chromablock and the split shape mode of the current chroma block is satisfied;and in response to a result of the determining, determining to not allowsplitting of the current chroma block, based on the split shape mode ofthe current chroma block, and determining at least one coding unitincluded in the current chroma block.

The condition based on the size or the area of the current chroma blockand the split shape mode of the current chroma block may correspond to acondition about whether a width or a height of the current chroma blockis equal to or smaller than 4 when a split type of the current chromablock indicates quad split.

The condition based on the size or the area of the current chroma blockand the split shape mode of the current chroma block may correspond to acondition about whether the area of the current chroma block is equal toor smaller than 16 when a split type of the current chroma blockindicates binary split.

The condition based on the size or the area of the current chroma blockand the split shape mode of the current chroma block may correspond to acondition about whether the area of the current chroma block is equal toor smaller than 32 when a split type of the current chroma blockindicates binary split.

The split shape mode of the blocks in the chroma image of the currentimage may be independent from the split shape mode of the blocksincluded in the luma image of the current image.

The split shape mode of the blocks in the chroma image of the currentimage may be dependent on a split shape mode of blocks in the luma imageof the current image, the blocks in the luma image corresponding to theblocks in the chroma image, and a size of the blocks in the chroma imagemay be determined based on a chroma sub sampling format of the currentimage and a size of the corresponding blocks in the luma image.

The image decoding method may further include, when a size of a blockfrom among a plurality of blocks to be generated by splitting thecurrent chroma block of the chroma image, based on the split shape modeof the current chroma block in the chroma image, is equal to or smallerthan 2×N (where N is an integer equal to or greater than 2) or N×2,determining to not allow splitting of the current chroma block based onthe split shape mode of the current chroma block, and determining atleast one coding unit included in the current chroma block.

The determining of the plurality of coding units in the luma image byhierarchically splitting the luma image based on the split shape mode ofthe blocks included in the luma image of the current image may include:when a current luma block included in the luma image is located at aright boundary of a picture, obtaining, from a bitstream, a flagindicating a split type from among binary split and quad split; anddetermining at least one coding unit included in the current luma block,based on the obtained flag.

According to an embodiment of the disclosure, an image decodingapparatus includes: at least one processor configured to determine aplurality of coding units in a luma image by hierarchically splittingthe luma image, based on a split shape mode of blocks included in theluma image of a current image, determine a plurality of coding units ina chroma image by hierarchically splitting the chroma image, based on asplit shape mode of blocks in the chroma image of the current image, anddecode the current image, based on the determined plurality of codingunits in the luma image and the determined plurality of coding units inthe chroma image, and wherein the split shape mode is a mode based on atleast one of a split direction and a split type of a block, and when theat least one processor determines the plurality of coding units in thechroma image, and when a size or an area of a chroma block from among aplurality of chroma blocks to be generated by splitting a current chromablock in the chroma image is equal to or smaller than a preset size or apreset area, the at least one processor is configured to not allowsplitting of the current chroma block based on a split shape mode of thecurrent chroma block, and determine at least one coding unit included inthe current chroma block.

According to an embodiment of the disclosure, an image encoding methodincludes: determining a plurality of coding units in a luma image byhierarchically splitting the luma image, based on a split shape mode ofblocks included in the luma image of a current image; determining aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks included in thechroma image of the current image; and encoding the current image, basedon the determined plurality of coding units in the luma image and thedetermined plurality of coding units in the chroma image, and whereinthe split shape mode is a mode based on at least one of a splitdirection and a split type of a block, and wherein the determining ofthe plurality of coding units in the chroma image includes, when a sizeor an area of a chroma block from among a plurality of chroma blocks tobe generated by splitting a current chroma block in the chroma image isequal to or smaller than a preset size or a preset area, not allowingsplitting of the current chroma block based on a split shape mode of thecurrent chroma block, and determining at least one coding unit includedin the current chroma block.

A computer program of an image encoding method or an image decodingmethod according to an embodiment of the disclosure may be recorded on acomputer-readable recording medium.

MODE OF DISCLOSURE

Advantages and features of embodiments and methods of accomplishing thesame may be understood more readily by reference to the embodiments andthe accompanying drawings. In this regard, the disclosure may havedifferent forms and should not be construed as being limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe concept of the disclosure to one of ordinary skill in the art.

The terms used in the specification will be briefly defined, and theembodiments will be described in detail.

All terms including descriptive or technical terms which are used in thespecification should be construed as having meanings that are obvious toone of ordinary skill in the art. However, the terms may have differentmeanings according to the intention of one of ordinary skill in the art,precedent cases, or the appearance of new technologies. Also, some termsmay be arbitrarily selected by the applicant, and in this case, themeaning of the selected terms will be described in detail in thedetailed description of the disclosure. Therefore, the terms used in thedisclosure should not be interpreted based on only their names but haveto be defined based on the meaning of the terms together with thedescriptions throughout the specification.

In the following specification, the singular forms include plural formsunless the context clearly indicates otherwise.

When a part “includes” or “comprises” an element, unless there is aparticular description contrary thereto, the part may further includeother elements, not excluding the other elements.

In the following descriptions, terms such as “unit” indicate software ora hardware component, and the “unit” performs certain functions.However, the “unit” is not limited to software or hardware. The “unit”may be formed so as to be in an addressable storage medium, or may beformed so as to operate one or more processors. Thus, for example, theterm “unit” may refer to components such as software components,object-oriented software components, class components, and taskcomponents, and may include processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,micro codes, circuits, data, a database, data structures, tables,arrays, or variables. A function provided by the components and “units”may be associated with the smaller number of components and “units”, ormay be divided into additional components and “units”.

According to an embodiment of the disclosure, “unit” may be implementedas a processor and a memory. The term “processor” should be interpretedbroadly to include a general purpose processor, a central processingunit (CPU), a microprocessor, a digital signal processor (DSP), acontroller, a microcontroller, a state machine, and the like. In someenvironments, the “processor” may refer to an application specificintegrated circuit (ASIC), a programmable logic device (PLD), a fieldprogrammable gate array (FPGA), or the like. The term “processor” mayrefer to a combination of processing devices such as, for example, acombination of a DSP and a microprocessor, a combination of a pluralityof microprocessors, a combination of one or more microprocessors inconjunction with a DSP core, or a combination of any other suchconfigurations.

The term “memory” should be interpreted broadly to include anyelectronic component capable of storing electronic information. The term“memory” may refer to various types of processor-readable media, such asrandom access memory (RAM), read-only memory (ROM), non-volatile randomaccess memory (NVRAM), programmable read-only memory (PROM),erase-programmable read-only memory (EPROM), electrically erasable PROM(EEPROM), flash memory, a magnetic or optical data storage device,registers, and the like. When the processor can read information from amemory and/or write information to the memory, the memory is stated tobe in an electronic communication state with the processor. The memoryintegrated in the processor is in an electronic communication state withthe processor.

Hereinafter, an “image” may be a static image such as a still image of avideo or may be a dynamic image such as a moving image, that is, thevideo itself.

Hereinafter, a “sample” denotes data assigned to a sampling position ofan image, i.e., data to be processed. For example, pixel values of animage in a spatial domain and transform coefficients on a transformdomain may be samples. A unit including at least one such sample may bedefined as a block.

Hereinafter, the disclosure will now be described more fully withreference to the accompanying drawings for one of ordinary skill in theart to be able to perform the embodiments without any difficulty. Inaddition, portions irrelevant to the description will be omitted in thedrawings for a clear description of the disclosure.

Hereinafter, an image encoding apparatus and an image decodingapparatus, and an image encoding method and an image decoding methodaccording to various embodiments will be described with reference toFIGS. 1 to 20 . With reference to FIGS. 3 to 16 , a method ofdetermining a data unit of an image according to various embodimentswill be described, and with reference to FIGS. 1 and 2 , and FIGS. 17 to20 , an image encoding apparatus and an image decoding apparatus, and animage encoding method and an image decoding method for encoding ordecoding an image based on various-shape coding units according tovarious embodiments will be described.

Hereinafter, an encoding or decoding method and apparatus for encodingor decoding an image based on various-shape coding units according to anembodiment of the disclosure will now be described with reference toFIGS. 1 and 2 .

FIG. 1A is a block diagram of an image decoding apparatus, according tovarious embodiments.

An image decoding apparatus 100 according to various embodiments mayinclude a coding unit determiner 105 and an image decoder 110. Thecoding unit determiner 105 and the image decoder 110 may include atleast one processor. Also, the coding unit determiner 105 and the imagedecoder 110 may include a memory storing instructions to be performed bythe at least one processor. The image decoder 110 and the coding unitdeterminer 105 may be implemented as separate hardware components, orthe image decoder 110 may include the coding unit determiner 105.

The coding unit determiner 105 may determine a plurality of coding unitsin a luma image by hierarchically splitting the luma image based on asplit shape mode of blocks included in the luma image of a currentimage.

The coding unit determiner 105 may determine a plurality of coding unitsin a chroma image by hierarchically splitting the chroma image based ona split shape mode of blocks included in the chroma image of the currentimage.

The coding unit determiner 105 may determine whether a size or area of achroma block is equal to or smaller than a preset size or area, whereinthe chroma block is from among a plurality of chroma blocks that may begenerated by splitting a current chroma block in the chroma image basedon a split shape mode of the current chroma block in the chroma image.The split shape mode of the current chroma block may refer to a modebased on at least one of a split direction and a split type of a block.

Based on a result of the determination, the coding unit determiner 105may determine to not allow splitting of the current chroma block basedon the split shape mode of the current chroma block.

The coding unit determiner 105 may determine at least one coding unitincluded in the current chroma block, based on one split shape mode fromamong split shape modes of the current block which are allowed exceptfor the split shape mode that is determined to not be allowed. When anallowed split shape mode of the current block does not exist, the codingunit determiner 105 may no longer perform splitting and may determinethe current chroma block to be a coding unit.

When the coding unit determiner 105 determines that the size or area ofthe chroma block is equal to or smaller than the preset size or area,wherein the chroma block is from among the plurality of chroma blocksthat may be generated by splitting the current chroma block in thechroma image based on the split shape mode of the current chroma blockin the chroma image, the coding unit determiner 105 may determine to notallow splitting of the current chroma block based on the split shapemode of the current chroma block. In this regard, the preset size may beone of 4×2, 2×4, and 2×2. Also, the preset area may be one of 8 and 4.

According to whether a condition based on a size or area of the currentchroma block and the split shape mode of the current chroma block issatisfied, the coding unit determiner 105 may determine whether the sizeor area of the chroma block is equal to or smaller than the preset sizeor area, wherein the chroma block is from among the plurality of chromablocks that may be generated by splitting the current chroma block inthe chroma image based on the split shape mode of the current chromablock in the chroma image. In this regard, the condition based on thesize or area of the current chroma block and the split shape modes ofthe current block may refer to a condition about whether a width orheight of the current chroma block is equal to or smaller than 4 when asplit type of the current chroma block indicates quad split. When thesplit type of the current chroma block indicates quad split and the sizeor width of the current chroma block is equal to or smaller than 4, thecoding unit determiner 105 may determine to not allow splitting based onquad split. That is, a height or width of a chroma block from among aplurality of chroma blocks generated by quad splitting the currentchroma block when the height or width of the current chroma block isequal to or smaller than 4 may be equal to or smaller than 2. Therefore,a size of the chroma block from among the plurality of chroma blocksgenerated by quad splitting the current chroma block may be 2×2, 4×2, or2×4 (or a smaller size), and when the size of such block is allowed as acoding unit and the block is encoded, a throughput may be decreased suchthat, in order to increase the throughput, quad split of the currentblock may be determined to not be allowed.

The coding unit determiner 105 may split the current chroma block basedon another allowed split type except for quad split. When an allowedsplit type for the current chroma block does not exist, the coding unitdeterminer 105 may no longer perform splitting and may determine thecurrent chroma block to be a coding unit.

The condition based on the size or area of the current chroma block andthe split shape modes of the current block may refer to a conditionabout whether an area of the current chroma block is equal to or smallerthan 16 when a split type of the current chroma block indicates binarysplit. When the split type of the current chroma block indicates binarysplit and the area of the current chroma block is equal to or smallerthan 16, the coding unit determiner 105 may determine to not allowsplitting based on binary split. That is, a size of a chroma block fromamong a plurality of chroma blocks generated by binary splitting thecurrent chroma block when the area of the current chroma block is equalto or smaller than 16 (e.g., when a size of the current chroma block isequal to or smaller than 2×8, 8×2, or 4×4) may be equal to or smallerthan 2×4, or 4×2. When the size of such block is allowed as a codingunit and the block is encoded, a throughput may be decreased such that,in order to increase the throughput, binary split of the current blockmay be determined to not be allowed. The coding unit determiner 105 maysplit the current chroma block based on another allowed split typeexcept for binary split. When an allowed split type for the currentchroma block does not exist, the coding unit determiner 105 may nolonger perform splitting and may determine the current chroma block tobe a coding unit.

The condition based on the size or area of the current chroma block andthe split shape modes of the current block may refer to a conditionabout whether an area of the current chroma block is equal to or smallerthan 32 when a split type of the current chroma block indicates trisplit (also referred to as the triple split). When the split type of thecurrent chroma block indicates tri split and the area of the currentchroma block is equal to or smaller than 32, the coding unit determiner105 may determine to not allow splitting based on tri split. That is, asize of a chroma block from among a plurality of chroma blocks generatedby tri splitting the current chroma block when the area of the currentchroma block is equal to or smaller than 32 (e.g., when a size of thecurrent chroma block is equal to or smaller than 4×8, 8×4, 2×16, or16×2) may be equal to or smaller than 2×4, or 4×2. When the size of suchblock is allowed as a coding unit and the block is encoded, a throughputmay be decreased such that, in order to increase the throughput, trisplit of the current block may be determined to not be allowed. Thecoding unit determiner 105 may split the current chroma block based onanother allowed split type except for tri split. When an allowed splittype for the current chroma block does not exist, the coding unitdeterminer 105 may no longer perform splitting and may determine thecurrent chroma block to be a coding unit.

A split shape mode of blocks in a chroma image of a current image may beindependent from a split shape mode of blocks included in a luma imageof the current image, but the disclosure is not limited thereto, andthus, the split shape mode of the blocks in the chroma image of thecurrent image may be dependent on a split shape mode of correspondingblocks included in a luma image of the current image which correspond tothe blocks in the chroma image.

That is, the coding unit determiner 105 may determine a plurality ofcoding units in the luma image by hierarchically splitting the lumaimage based on the split shape mode of the blocks included in the lumaimage of the current image, and may determine a plurality of codingunits in the chroma image by hierarchically splitting the chroma image,based on a split shape mode of blocks included in the chroma image whichis equal to the split shape mode of the blocks included in the lumaimage. In this regard, the coding unit determiner 105 may determine asize of a block in the chroma image, based on a chroma sub samplingscheme of the current block and a size of a corresponding block of theluma image. For example, when the chroma sub sampling scheme refers toYUV 4:2:0, and the size of the corresponding block of the luma imagerefers to 16×16, the size of the block in the chroma image may bedetermined to be 8×8.

When a size of a block is equal to or smaller than 2×N (where N is aninteger equal to or greater than 2) or N×2, wherein the block is fromamong a plurality of blocks generated by splitting the current chromablock in the chroma image based on the split shape mode of the currentchroma block in the chroma image, the coding unit determiner 105 maydetermine to not allow splitting of the current chroma block based onthe split shape mode of the current chroma block. The coding unitdeterminer 105 may determine at least one coding unit included in thecurrent chroma block based on allowable split types excluding thedisallowed split type.

The image decoder 110 may decode the current image, based on theplurality of coding units in the luma image and the plurality of codingunits in the chroma image.

Each of luma blocks split from each inter slice or picture may have adifferent prediction mode. For example, each luma block may have aninter or intra prediction mode. In this case, the image decodingapparatus 100 may determine a prediction mode of a corresponding chromablock to be as below. When a current slice or picture is an inter sliceor picture, and a ratio of an area of a luma block having an intraprediction mode to an area of a luma block is equal to or greater than apreset value, the image decoding apparatus 100 may determine aprediction mode of a chroma block to be an intra prediction mode.

When a current slice or picture is an inter slice or picture, and aratio of an area of a luma block having an inter prediction mode to anarea of a luma block is equal to or greater than a preset value, theimage decoding apparatus 100 may determine a prediction mode of a chromablock to be an inter prediction mode.

When a luma block having a particular size is split, the image decodingapparatus 100 may obtain, from a bitstream, information about aprediction mode of a corresponding chroma block.

The image decoding apparatus 100 may determine a prediction mode of aluma block to be a prediction mode of a chroma block, the luma blockcorresponding to a particular location of the chroma block. For example,the particular location may be an upper-left location, a centerlocation, a lower-left location, a top location, a lower-right location,and the like. In this regard, the particular location may be apredefined location, but the disclosure is not limited thereto, and theimage decoding apparatus 100 may obtain information about the particularlocation from a separate bitstream, and may determine the particularlocation based on the obtained information.

In order to improve a throughput, the image decoding apparatus 100 mayperform operations below when a size of a current block is equal to orsmaller than a particular size or an area of the current block is equalto or smaller than a particular value.

The image decoding apparatus 100 may inverse transform the current blockby using a transformation method other than a transformation method suchas a Discrete Cosine Transform (DCT). For example, when the size of thecurrent block is smaller than 4×4, the image decoder 110 may inversetransform the current block by using the Hadamard transform.

The image decoding apparatus 100 may set a value of a transform skipflag about the current block to be constantly 1. For example, the imagedecoding apparatus 100 may obtain a transform skip flag about thecurrent block from a bitstream, and may set a value of the transformskip flag based on the value of the transform skip flag obtained fromthe bitstream. However, when the size of the current block is equal toor smaller than a particular size or the area of the current block isequal to or smaller than a particular value, the image decodingapparatus 100 may not obtain the transform skip flag from the bitstreamand may set the value of the transform skip flag about the current blockto be 1.

The transform skip flag refers to a flag indicating whethertransformation is to be used, and when the value of the transform skipflag is 0, the image decoding apparatus 100 may not perform aninverse-transformation operation and may reconstruct the current blockby using a de-quantized block, and when the value is 1, the imagedecoding apparatus 100 may generate an inverse-transformed block byperforming the inverse-transformation operation on the de-quantizedblock, and may reconstruct the current block by using theinverse-transformed block.

When a size of a block is equal to or smaller than a particular size orarea, the image decoding apparatus 100 may determine to not allowsplitting of the block. For example, when the size of the current blockis 8×8, the image decoding apparatus 100 may determine to not allowsplitting of the current block. Also, for example, when the area of thecurrent block is 64, the image decoding apparatus 100 may determine tonot allow splitting of the current block.

In an inter slice or picture, a probability that a block is to be splitmay be smaller than a probability that the block is to be skipped, andthus the image decoding apparatus 100 may perform operations below.

The image decoding apparatus 100 may first obtain split information ofthe current block from a bitstream, before split information of thecurrent block.

The image decoding apparatus 100 may obtain flag information indicatingwhether a largest coding unit has residual information at a largestcoding unit level, and when a value of the flag information indicatesthat the largest coding unit does not have the residual information, theimage decoding apparatus 100 may not parse, from a bitstream, syntaxelements related to residual, and may determine to skip a decodingprocess related thereto.

Also, in an inter slice or picture, the image decoding apparatus 100 maydetermine to not allow asymmetrical binary split.

When the current block is located at a boundary of a picture, the imagedecoding apparatus 100 may split the current block without separatelyobtaining information from a bitstream. For example, when the currentblock is located at the boundary of the picture, the image decodingapparatus 100 may quad split the current block without separatelyobtaining information from the bitstream. In this regard, the currentblock may be recursively quad split until split blocks are not locatedat the boundary. However, in a case where a predetermined split depth ispresent, a block may be split to the depth.

When the current block is located at the boundary of the picture, theimage decoding apparatus 100 may split the current block withoutseparately obtaining information from the bitstream, and in this regard,the image decoding apparatus 100 may split the current block based onvarious split types and split directions. In this regard, the imagedecoding apparatus 100 may determine a split type and a split directionof the current block, based on a boundary condition of a block. In thisregard, the current block may be recursively quad split until splitblocks are not located at the boundary. However, in a case where apredetermined split depth is present, a block may be split to the depth.

For example, when the current block is located at a bottom boundary of apicture, the image decoding apparatus 100 may determine the splitdirection of the current block to be a horizontal direction, maydetermine the split type to be binary split (or tri split), and maybinary split (tri split) the current block in the horizontal direction,based on the split direction and the split type of the current block.

When the current block is located at a right boundary of the picture,the image decoding apparatus 100 may determine the split direction ofthe current block to be a vertical direction, may determine the splittype to be binary split (or tri split), and may binary split (tri split)the current block in the vertical direction, based on the splitdirection and the split type of the current block.

When the current block is located at a lower-right boundary of thepicture, the image decoding apparatus 100 may determine the split typeof the current block to be quad split, and may quad split the currentblock, based on the split type of the current block.

Because split types or split directions which are allowable for a blockbecome various, complexity is geometrically increased. In order todecrease the complexity, the image decoding apparatus 100 may restrictsome split types or split directions from among the various split typesor split directions.

For example, the image decoding apparatus 100 may restrict a split depthof binary split. The image decoding apparatus 100 may restrict anallowable ratio of the block or an allowable size of the block.

The image decoding apparatus 100 may split the block by using only asplit shape mode that satisfies the restriction condition, withoutseparately obtaining information from a bitstream.

When the current block is located at a boundary of the picture, theimage decoding apparatus 100 may allow only some split types from amongthe various split types of the block. For example, when the currentblock is located at the boundary of the picture, the image decodingapparatus 100 may allow only quad split from among the various splittypes.

In a case where a particular split shape mode being usable in thecurrent block does not exist, the image decoding apparatus 100 mayimplicitly split the current block until split blocks have a particularsplit shape mode being usable in the block.

When the current block located at the boundary of the picture does nothave residual, the image decoding apparatus 100 may determine to notfurther split the current block. In order to enable the determination,the image decoding apparatus 100 may perform operations below.

When the current block is located at the boundary of the picture, theimage decoding apparatus 100 may obtain, from a bitstream, a flagindicating whether implicit split with respect to the current block isallowed. When a value of the flag is equal to 0, the image decodingapparatus 100 may determine that implicit split with respect to thecurrent block is not allowed. In this case, the image decoding apparatus100 may obtain information about a split shape mode of the current blockfrom a bitstream, and may determine the split shape mode of the currentblock, based on the obtained information. When a value of the flag isequal to 1, the image decoding apparatus 100 may determine that implicitsplit with respect to the current block is allowed. In this case, theimage decoding apparatus 100 may perform implicit split on the currentblock.

When the current block is located at the boundary of the picture, theimage decoding apparatus 100 may obtain, from a bitstream, a flagindicating that the current block does not have residual. When a valueof the flag is equal to 0, the image decoding apparatus 100 may performimplicit split on the current block. When a value of the flag is equalto 1, the image decoding apparatus 100 may determine to perform a skipmode decoding process on the current block.

When a current largest coding unit is located at the boundary of thepicture, the image decoding apparatus 100 may obtain a flag of a largestcoding unit level from a bitstream, the flag indicating whether implicitsplit is allowed for a largest coding unit.

When a value of the flag is 0, the image decoding apparatus 100 maydetermine to not allow implicit split for the largest coding unit.

When a value of the flag is 1, the image decoding apparatus 100 maydetermine to allow implicit split for the largest coding unit, and mayperform an implicit split process on the largest coding unit.

When the current largest coding unit is located at the boundary of thepicture, the image decoding apparatus 100 may obtain, from a bitstream,a flag indicating that the current largest coding unit does not haveresidual. When a value of the flag is equal to 0, the image decodingapparatus 100 may perform implicit split on the current largest codingunit. When a value of the flag is equal to 1, the image decodingapparatus 100 may determine to perform a skip mode decoding process onthe current largest coding unit.

When the current block is located at the boundary of the picture, theimage decoding apparatus 100 may implicitly determine a split shape modeof the current block. For example, the image decoding apparatus 100 maydetermine one split shape mode from among a plurality of particularsplit shape modes, based on a boundary condition. When the current blockis located at a right boundary of the picture, the image decodingapparatus 100 may obtain, from a bitstream, a flag indicating one splittype from among binary split and quad split.

When the current largest coding unit is located at the boundary of thepicture, the image decoding apparatus 100 may obtain, from a bitstream,split shape mode information to be used for the current largest codingunit.

When the current block is located at the boundary of the picture, theimage decoding apparatus 100 may determine a split shape mode of thecurrent block, based on a ratio of an area in the picture. For example,the image decoding apparatus 100 may determine a split shape mode of thecurrent block, based on a ratio of a height and a width of a block areain the picture. When the current block is located at a left boundary ora right boundary, and a ratio of a width and a height of the currentblock is greater than N, the image decoding apparatus 100 may determinea split type of the current block to be quad split. If it is not so, theimage decoding apparatus 100 may determine the split type of the currentblock to be binary split.

When the ratio of the width and the height of the current block is notequal to an integer value, the image decoding apparatus 100 maydetermine the split type of the current block to be quad split or maydetermine the split type of the current block to be binary split.

Alternatively, regardless of whether the current block is located at theboundary of the picture, the image decoding apparatus 100 may alwaysobtain the split shape mode information about the current block from abitstream. When the current block is located at the boundary of thepicture, the image decoding apparatus 100 may determine to performentropy decoding by allocating context-adaptive binary arithmetic coding(CABAC) context different from context of blocks that are not located atthe boundary of the picture. The image decoding apparatus 100 maydetermine to perform entropy decoding by using CABAC context based on aboundary condition.

FIG. 1B is a flowchart of an image decoding method, according to variousembodiments.

In operation S105, the image decoding apparatus 100 may determine aplurality of coding units in a luma image by hierarchically splittingthe luma image, based on a split shape mode of blocks included in theluma image of a current image. The split shape mode may be a mode basedon at least one of a split direction and a split type. The split typemay indicate at least one of binary split, tri split, and quad split.

In operation S110, the image decoding apparatus 100 may determine aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks included in thechroma image of the current image. When a size or area of a chroma blockis equal to or smaller than a preset size or area, wherein the chromablock is from among a plurality of chroma blocks that may be generatedby splitting a current chroma block in the chroma image based on a splitshape mode of the current chroma block in the chroma image, the imagedecoding apparatus 100 may not allow splitting of the current chromablock based on a split shape mode of the current chroma block and maydetermine at least one coding unit included in the current chroma block.

In operation S115, the image decoding apparatus 100 may decode thecurrent image, based on the plurality of coding units in the luma imageand the plurality of coding units in the chroma image.

FIG. 1C is a block diagram of an image decoder 6000 according to variousembodiments.

The image decoder 6000 according to various embodiments performsoperations necessary for the image decoder 110 of the image decodingapparatus 100 to decode image data.

Referring to FIG. 1C, an entropy decoder 6150 parses, from a bitstream6050, encoded image data to be decoded, and encoding informationnecessary for decoding. The encoded image data is a quantized transformcoefficient, and a de-quantizer 6200 and an inverse-transformer 6250reconstruct residue data from the quantized transform coefficient.

An intra predictor 6400 performs intra prediction on each of blocks. Aninter predictor 6350 performs inter prediction on each block by using areference image obtained from a reconstructed picture buffer 6300. Dataof a spatial domain for a block of a current image 6050 may bereconstructed by adding residual data and prediction data of each blockwhich are generated by the intra predictor 6400 or the inter predictor6350, and a deblocker 6450 and a sample adaptive offset (SAO) performer6500 may perform loop filtering on the reconstructed data of the spatialdomain, such that a filtered reconstructed image may be output.Reconstructed images stored in the reconstructed picture buffer 6300 maybe output as a reference image.

In order for the image decoding apparatus 100 to encode the image data,the image decoder 6000 according to various embodiments may performoperations of each stage on each block.

FIG. 2A is a block diagram of an image encoding apparatus, according tovarious embodiments.

An image encoding apparatus 150 according to various embodiments mayinclude a coding unit determiner 155 and an image encoder 160.

The coding unit determiner 155 and the image encoder 160 may include atleast one processor. Also, the coding unit determiner 155 and the imageencoder 160 may include a memory storing instructions to be performed bythe at least one processor. The image encoder 160 and the coding unitdeterminer 155 may be implemented as separate hardware components, orthe image encoder 160 may include the coding unit determiner 155.

The coding unit determiner 155 may determine a plurality of coding unitsin a luma image by hierarchically splitting the luma image based on asplit shape mode of blocks included in the luma image of a currentimage.

The coding unit determiner 155 may determine a plurality of coding unitsin a chroma image by hierarchically splitting the chroma image based ona split shape mode of blocks included in the chroma image of the currentimage. The coding unit determiner 155 may determine whether a size orarea of a chroma block is equal to or smaller than a preset size orarea, wherein the chroma block is from among a plurality of chromablocks that may be generated by splitting a current chroma block in thechroma image based on a split shape mode of the current chroma block inthe chroma image. Based on a result of the determination, the codingunit determiner 155 may determine to not allow splitting of the currentchroma block based on the split shape mode of the current chroma block.

The coding unit determiner 155 may determine at least one coding unitincluded in the current chroma block, based on one split shape mode fromamong split shape modes of the current block which are allowed exceptfor the split shape mode that is determined to not be allowed. When anallowed split shape mode of the current block does not exist, the codingunit determiner 155 may no longer perform splitting and may determinethe current chroma block to be a coding unit.

When the coding unit determiner 155 determines that the size or area ofthe chroma block is equal to or smaller than the preset size or area,wherein the chroma block is from among the plurality of chroma blocksthat may be generated by splitting the current chroma block in thechroma image based on the split shape mode of the current chroma blockin the chroma image, the coding unit determiner 155 may determine to notallow splitting of the current chroma block based on the split shapemode of the current chroma block. In this regard, the preset size may beone of 4×2, 2×4, and 2×2. Also, the preset area may be one of 8 and 4.

According to whether a condition based on a size or area of the currentchroma block and the split shape mode of the current chroma block issatisfied, the coding unit determiner 155 may determine whether the sizeor area of the chroma block is equal to or smaller than the preset sizeor area, wherein the chroma block is from among the plurality of chromablocks that may be generated by splitting the current chroma block inthe chroma image based on the split shape mode of the current chromablock in the chroma image. In this regard, the condition based on thesize or area of the current chroma block and the split shape modes ofthe current block may refer to a condition about whether a width orheight of the current chroma block is equal to or smaller than 4 when asplit type of the current chroma block indicates quad split. When thesplit type of the current chroma block indicates quad split and the sizeor width of the current chroma block is equal to or smaller than 4, thecoding unit determiner 155 may determine to not allow splitting based onquad split. That is, a height or width of a chroma block from among aplurality of chroma blocks generated by quad splitting the currentchroma block when the height or width of the current chroma block isequal to or smaller than 4 may be equal to or smaller than 2. Therefore,a size of the chroma block from among the plurality of chroma blocksgenerated by quad splitting the current chroma block may be 2×2, 4×2, or2×4 (or a smaller size), and when the size of such block is allowed as acoding unit and the block is encoded, a throughput may be decreased suchthat, in order to increase the throughput, quad split of the currentblock may be determined to not be allowed. The coding unit determiner155 may split the current chroma block based another allowed split typeexcept for quad split. When an allowed split type for the current chromablock does not exist, the coding unit determiner 155 may no longerperform splitting and may determine the current chroma block to be acoding unit.

The condition based on the size or area of the current chroma block andthe split shape modes of the current block may refer to a conditionabout whether an area of the current chroma block is equal to or smallerthan 16 when a split type of the current chroma block indicates binarysplit. When the split type of the current chroma block indicates binarysplit and the area of the current chroma block is equal to or smallerthan 16, the coding unit determiner 155 may determine to not allowsplitting based on binary split. That is, a size of a chroma block fromamong a plurality of chroma blocks generated by binary splitting thecurrent chroma block when the area of the current chroma block is equalto or smaller than 16 (e.g., when a size of the current chroma block isequal to or smaller than 2×8, 8×2, or 4×4) may be equal to or smallerthan 2×4, or 4×2. When the size of such block is allowed as a codingunit and the block is encoded or decoded, a throughput may be decreasedsuch that, in order to increase the throughput, binary split of thecurrent block may be determined to not be allowed. The coding unitdeterminer 155 may split the current chroma block based on anotherallowed split type except for binary split. When an allowed split typefor the current chroma block does not exist, the coding unit determiner155 may no longer perform splitting and may determine the current chromablock to be a coding unit.

The condition based on the size or area of the current chroma block andthe split shape modes of the current block may refer to a conditionabout whether an area of the current chroma block is equal to or smallerthan 32 when a split type of the current chroma block indicates trisplit. When the split type of the current chroma block indicates trisplit and the area of the current chroma block is equal to or smallerthan 32, the coding unit determiner 155 may determine to not allowsplitting based on tri split. That is, a size of a chroma block fromamong a plurality of chroma blocks generated by tri splitting thecurrent chroma block when the area of the current chroma block is equalto or smaller than 32 (e.g., when a size of the current chroma block isequal to or smaller than 4×8, 8×4, 2×16, or 16×2) may be equal to orsmaller than 2×4, or 4×2. When the size of such block is allowed as acoding unit and the block is encoded or decoded, a throughput may bedecreased such that, in order to increase the throughput, tri split ofthe current block may be determined to not be allowed. The coding unitdeterminer 155 may split the current chroma block based on anotherallowed split type except for tri split. When an allowed split type forthe current chroma block does not exist, the coding unit determiner 155may no longer perform splitting and may determine the current chromablock to be a coding unit.

A split shape mode of blocks in a chroma image of a current image may beindependent from a split shape mode of blocks included in a luma imageof the current image, but the disclosure is not limited thereto, andthus, the split shape mode of the blocks in the chroma image of thecurrent image may be dependent on a split shape mode of correspondingblocks included in a luma image of the current image which correspond tothe blocks in the chroma image.

That is, the coding unit determiner 155 may determine a plurality ofcoding units in the luma image by hierarchically splitting the lumaimage based on the split shape mode of the blocks included in the lumaimage of the current image, and may determine a plurality of codingunits in the chroma image by hierarchically splitting the chroma image,based on a split shape mode of blocks included in the chroma image whichis equal to the split shape mode of the blocks included in the lumaimage. In this regard, the coding unit determiner 155 may determine asize of a block in the chroma image, based on a chroma sub samplingscheme of the current block and a size of a corresponding block of theluma image. For example, when the chroma sub sampling scheme refers toYUV 4:2:0, and the size of the corresponding block of the luma imagerefers to 16×16, the size of the block in the chroma image may bedetermined to be 8×8.

When a size of a block is equal to or smaller than 2×N (where N is aninteger equal to or greater than 2) or N×2, wherein the block is fromamong a plurality of blocks split from the current chroma block in thechroma image based on the split shape mode of the current chroma blockin the chroma image, the coding unit determiner 155 may determine to notallow splitting of the current chroma block based on the split shapemode of the current chroma block. The coding unit determiner 155 maydetermine at least one coding unit included in the current chroma blockbased on allowable split types excluding the disallowed split type.

The image encoder 160 may encode the current image, based on theplurality of coding units in the luma image and the plurality of codingunits in the chroma image.

Each of luma blocks split from each inter slice or picture may have adifferent prediction mode. For example, each luma block may have aninter or intra prediction mode. In this case, the image encodingapparatus 150 may determine a prediction mode of a corresponding chromablock to be as below. When a current slice or picture is an inter sliceor picture, and a ratio of an area of a luma block having an intraprediction mode to an area of a luma block is equal to or greater than apreset value, the image encoding apparatus 150 may determine aprediction mode of a chroma block to be an intra prediction mode.

When a current slice or picture is an inter slice or picture, and aratio of an area of a luma block having an inter prediction mode to anarea of a luma block is greater than a preset value, the image encodingapparatus 150 may determine a prediction mode of a chroma block to be aninter prediction mode.

When a luma block having a particular size is split, the image encodingapparatus 150 may encode information about a prediction mode of acorresponding chroma block, and may generate a bitstream including theencoded information about the prediction mode of the chroma block.

The image encoding apparatus 150 may determine a prediction mode of aluma block to be a prediction mode of a chroma block, the luma blockcorresponding to a particular location of the chroma block. For example,the particular location may be an upper-left location, a centerlocation, a lower-left location, a top location, a lower-right location,and the like. In this regard, the particular location may be apredefined location, but the disclosure is not limited thereto, and theimage encoding apparatus 150 may encode information about the particularlocation, and may generate a bitstream including the encoded informationabout the particular location.

In order to improve a throughput, the image encoding apparatus 150 mayperform operations below when a size of a current block is equal to orsmaller than a particular size or an area of the current block is equalto or smaller than a particular value.

The image encoding apparatus 150 may transform the current block byusing a transformation method other than a transformation method such asa DCT. For example, when the size of the current block is smaller than4×4, the image encoding apparatus 150 may transform the current block byusing the Hadamard transform.

The image encoding apparatus 150 may determine to skip transformation ofthe current block. For example, the image encoding apparatus 150 mayencode a transform skip flag and may generate a bitstream including theencoded flag. However, when the size of the current block is equal to orsmaller than a particular size or the area of the current block is equalto or smaller than a particular value, the image encoding apparatus 150may determine to skip transformation of the current block and may notencode the transform skip flag about the current block.

When a size of a block is equal to or smaller than a particular size orarea, the image encoding apparatus 150 may determine to not allowsplitting of the block. For example, when the size of the current blockis 8×8, the image encoding apparatus 150 may determine to not allowsplitting of the current block. Also, for example, when the area of thecurrent block is 64, the image encoding apparatus 150 may determine tonot allow splitting of the current block.

When a current slice or picture is an inter slice or picture, aprobability that a block is to be split may be less than a probabilitythat the block is to be skipped, and thus, the image encoding apparatus150 may perform operations below.

The image encoding apparatus 150 may first encode split information ofthe current block before split information of the current block.

When the image encoding apparatus 150 determines that a largest codingunit does not have residual information, the image encoding apparatus150 may determine to not encode syntax elements related to residual, mayencode a flag indicating that the largest coding unit does not have theresidual information, and may generate a bitstream including the encodedflag.

When a current slice or picture is an inter slice or picture, the imageencoding apparatus 150 may determine to not allow asymmetrical binarysplit.

When the current block is located at a boundary of a picture, the imageencoding apparatus 150 may split the current block. In this regard, theimage encoding apparatus 150 may not encode split shape mode informationabout the current block.

For example, when the current block is located at the boundary of thepicture, the image encoding apparatus 150 may quad split the currentblock without separately encoding split shape mode information. In thisregard, the current block may be recursively quad split until splitblocks are not located at the boundary. However, in a case where apredetermined split depth is present, a block may be split to the depth.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may split the current block withoutseparately encoding split shape mode information about the currentblock, and in this regard, the image encoding apparatus 150 may splitthe current block based on various split types and split directions. Inthis regard, the image encoding apparatus 150 may determine a split typeand a split direction of the current block, based on a boundarycondition of a block. In this regard, the current block may berecursively quad split until split blocks are not located at theboundary. However, in a case where a predetermined split depth ispresent, a block may be split to the depth.

For example, when the current block is located at a bottom boundary of apicture, the image encoding apparatus 150 may determine the splitdirection of the current block to be a horizontal direction, maydetermine the split type to be binary split, and may binary split thecurrent block in the horizontal direction, based on the split directionand the split type of the current block.

When the current block is located at a right boundary of the picture,the image encoding apparatus 150 may determine the split direction ofthe current block to be a vertical direction, may determine the splittype to be binary split, and may binary split the current block in thevertical direction, based on the split direction and the split type ofthe current block.

When the current block is located at a lower-right boundary of thepicture, the image encoding apparatus 150 may determine the split typeof the current block to be quad split, and may quad split the currentblock, based on the split type of the current block.

Because split types or split directions which are allowable for a blockbecome various, complexity is geometrically increased. In order todecrease the complexity, the image encoding apparatus 150 may restrictsome split types or split directions from among the various split typesor split directions.

For example, the image encoding apparatus 150 may restrict a split depthof binary split. The image encoding apparatus 150 may restrict anallowable ratio of the block or an allowable size of the block.

The image encoding apparatus 150 may split the block by using only asplit shape mode that satisfies the restriction condition, and may notseparately encode split shape mode information.

When the current block is located at a boundary of the picture, theimage encoding apparatus 150 may allow only some split types from amongthe various split types of the block. For example, when the currentblock is located at the boundary of the picture, the image encodingapparatus 150 may allow only quad split from among the various splittypes.

In a case where a particular split shape mode being usable in thecurrent block does not exist, the image encoding apparatus 150 mayimplicitly split the current block until split blocks have a particularsplit shape mode being usable in the block.

When the current block located at the boundary of the picture does nothave residual, the image encoding apparatus 150 may determine to notfurther split the current block. In order to enable the determination,the image encoding apparatus 150 may perform operations below.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may encode a flag indicating whetherimplicit split with respect to the current block is allowed. When theimage encoding apparatus 150 determines to not allow implicit split withrespect to the current block, the image encoding apparatus 150 mayencode a value of the flag as 0. In this case, the image encodingapparatus 150 may encode split shape mode information about the currentblock, and may generate a bitstream including the encoded split shapemode information about the current block.

When the image encoding apparatus 150 determines to allow implicit splitwith respect to the current block, the image encoding apparatus 150 mayencode a value of the flag as 1.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may encode a flag indicating that thecurrent block does not have residual, and may generate a bitstreamincluding the encoded flag.

When the image encoding apparatus 150 performs implicit split on thecurrent block, the image encoding apparatus 150 may encode a value ofthe flag as 0. When the image encoding apparatus 150 performs a skipmode encoding process on the current block, the image encoding apparatus150 may encode a value of the flag as 1.

When a current largest coding unit is located at the boundary of thepicture, the image encoding apparatus 150 may encode a flag of a largestcoding unit level, the flag indicating whether implicit split is allowedfor a largest coding unit.

When the image encoding apparatus 150 determines to not allow implicitsplit with respect to the largest coding unit, the image encodingapparatus 150 may encode a value of the flag as 0.

When the image encoding apparatus 150 performs an implicit split processon the largest coding unit, the image encoding apparatus 150 may encodea value of the flag as 1.

When the current largest coding unit is located at the boundary of thepicture, the image encoding apparatus 150 may encode a flag indicatingthat the current largest coding unit does not have residual. When theimage encoding apparatus 150 performs implicit split on the currentlargest coding unit, the image encoding apparatus 150 may encode a valueof the flag to be equal to 0. When the image encoding apparatus 150determines to perform a skip mode encoding process on the currentlargest coding unit, the image encoding apparatus 150 may encode a valueof the flag to be equal to 1.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may implicitly determine a split shape modeof the current block. For example, the image encoding apparatus 150 maydetermine one split shape mode from among a plurality of particularsplit shape modes, based on a boundary condition. When the current blockis located at a right boundary of the picture, the image encodingapparatus 150 may encode a flag indicating one split type from amongbinary split and quad split.

When the current largest coding unit is located at the boundary of thepicture, the image encoding apparatus 150 may encode split shape modeinformation to be used for the current largest coding unit, and maygenerate a bitstream including the encoded split shape mode information.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may determine a split shape mode of thecurrent block, based on a ratio of an area in the picture. For example,the image encoding apparatus 150 may determine a split shape mode of thecurrent block, based on a ratio of a height and a width of a block areain the picture. When the current block is located at a left boundary ora right boundary, and a ratio of a width and a height of the currentblock is greater than N, the image encoding apparatus 150 may determinea split type of the current block to be quad split. If it is not so, theimage encoding apparatus 150 may determine the split type of the currentblock to be binary split.

When the ratio of the width and the height of the current block is notequal to an integer value, the image encoding apparatus 150 maydetermine the split type of the current block to be quad split or maydetermine the split type of the current block to be binary split.

Alternatively, regardless of whether the current block is located at theboundary of the picture, the image encoding apparatus 150 may encode thesplit shape mode information about the current block.

When the current block is located at the boundary of the picture, theimage encoding apparatus 150 may entropy encode the current block byallocating CABAC context different from context of blocks that are notlocated at the boundary of the picture. The image encoding apparatus 150may perform entropy encoding by using CABAC context based on a boundarycondition.

FIG. 2B illustrates a flowchart of an image encoding method according tovarious embodiments.

In operation S155, the image encoding apparatus 150 may determine aplurality of coding units in a luma image by hierarchically splittingthe luma image, based on a split shape mode of blocks included in theluma image of a current image.

In operation S160, the image encoding apparatus 150 may determine aplurality of coding units in a chroma image by hierarchically splittingthe chroma image, based on a split shape mode of blocks included in thechroma image of the current image. When a size or area of a chroma blockis equal to or smaller than a preset size or area, wherein the chromablock is from among a plurality of chroma blocks that may be generatedby splitting a current chroma block in the chroma image based on a splitshape mode of the current chroma block in the chroma image, the imageencoding apparatus 150 may not allow splitting of the current chromablock based on a split shape mode of the current chroma block and maydetermine at least one coding unit included in the current chroma block.

In operation S165, the image encoding apparatus 150 may encode thecurrent image, based on the plurality of coding units in the luma imageand the plurality of coding units in the chroma image.

FIG. 2C is a block diagram of an image encoder according to variousembodiments.

An image encoder 7000 according to various embodiments performsoperations necessary for the image encoder 160 of the image encodingapparatus 150 to encode image data.

That is, an intra predictor 7200 performs intra prediction on each ofblocks of a current image 7050, and an inter predictor 7150 performsinter prediction on each of the blocks by using the current image 7050and a reference image obtained from a reconstructed picture buffer 7100.

Prediction data is subtracted from data of a block to be encoded in thecurrent image 7050, wherein the prediction data is related to each blockand is output from the intra predictor 7200 or the inter predictor 7150,and the transformer 7250 and the quantizer 7300 may output a quantizedtransform coefficient of each block by performing transformation andquantization on the residue data. A de-quantizer 7450 and aninverse-transformer 7500 may reconstruct residue data of a spatialdomain by performing de-quantization and inverse transformation on thequantized transform coefficient. The reconstructed residue data of thespatial domain may be added to the prediction data that is related toeach block and is output from the intra predictor 7200 or the interpredictor 7150, and thus may be reconstructed as data of a spatialdomain with respect to a block of the current image 7050. A deblocker7550 and a SAO performer 7600 generate a filtered reconstructed image byperforming inloop filtering on the reconstructed data of the spatialdomain. The generated reconstructed image is stored in the reconstructedpicture buffer 7100. Reconstructed images stored in the reconstructedpicture buffer 7100 may be used as a reference image for interprediction with respect to another image. An entropy encoder 7350 mayentropy encode the quantized transform coefficient, and the entropyencoded coefficient may be output as a bitstream 7400.

In order for the image encoder 7000 according to various embodiments tobe applied to the image encoding apparatus 150, the image encoder 7000according to various embodiments may perform operations of each stage oneach block.

Hereinafter, splitting of a coding unit will be described in detailaccording to an embodiment of the disclosure.

An image may be split into largest coding units. A size of each largestcoding unit may be determined based on information obtained from abitstream. A shape of each largest coding unit may be a square shape ofthe same size. However, the disclosure is not limited thereto. Also, alargest coding unit may be hierarchically split into coding units basedon split shape mode information obtained from the bitstream. The splitshape mode information may include at least one of informationindicating whether splitting is to be performed, split directioninformation, and split type information. The information indicatingwhether splitting is to be performed indicates whether a coding unit isto be split. The split direction information indicates that splitting isto be performed in one of a horizontal direction or a verticaldirection. The split type information indicates that a coding unit is tobe split by using one of binary split, tri split (also referred to astriple split), or quad split.

For convenience of description, in the disclosure, it is assumed thatthe split shape mode information includes the information indicatingwhether splitting is to be performed, the split direction information,and the split type information, but the disclosure is not limitedthereto. The image decoding apparatus 100 may obtain, from a bitstream,the split shape mode information as one bin string. The image decodingapparatus 100 may determine whether to split a coding unit, a splitdirection, and a split type, based on the one bin string.

The coding unit may be equal to or smaller than a largest coding unit.For example, when the split shape mode information indicates thatsplitting is not to be performed, the coding unit has a same size as thelargest coding unit. When the split shape mode information indicatesthat splitting is to be performed, the largest coding unit may be splitinto lower-depth coding units. When split shape mode information aboutthe lower-depth coding units indicates splitting, the lower-depth codingunits may be split into smaller coding units. However, the splitting ofthe image is not limited thereto, and the largest coding unit and thecoding unit may not be distinguished. The splitting of the coding unitwill be described in detail with reference to FIGS. 3 to 16 .

Also, the coding unit may be split into prediction units for predictionof the image. The prediction units may each be equal to or smaller thanthe coding unit. Also, the coding unit may be split into transform unitsfor transformation of the image. The transform units may each be equalto or smaller than the coding unit. Shapes and sizes of the transformunit and the prediction unit may not be related to each other. Thecoding unit may be distinguished from the prediction unit and thetransform unit, or the coding unit, the prediction unit, and thetransform unit may be equal to each other. Splitting of the predictionunit and the transform unit may be performed in a same manner assplitting of the coding unit. The splitting of the coding unit will bedescribed in detail with reference to FIGS. 3 to 16 . A current blockand a neighboring block of the disclosure may indicate one of thelargest coding unit, the coding unit, the prediction unit, and thetransform unit. Also, the current block of the current coding unit is ablock that is currently being decoded or encoded or a block that iscurrently being split. The neighboring block may be a blockreconstructed prior to the current block. The neighboring block may bespatially or temporally adjacent to the current block. The neighboringblock may be located at one of the lower-left, left, upper-left, top,upper-right, right, lower-right of the current block.

FIG. 3 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a currentcoding unit, according to an embodiment.

A block shape may include 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N,16N×N, N×16N, 8N×N, or N×8N. Here, N may be a positive integer. Blockshape information is information indicating at least one of a shape,direction, a ratio of a width and height, or sizes of the coding unit.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are equal (i.e.,when the block shape of the coding unit is 4N×4N), the image decodingapparatus 100 may determine the block shape information of the codingunit as a square. The image decoding apparatus 100 may determine theshape of the coding unit to be a non-square.

When the lengths of the width and the height of the coding unit aredifferent from each other (i.e., when the block shape of the coding unitis 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, orN×8N), the image decoding apparatus 100 may determine the block shapeinformation of the coding unit as a non-square shape. When the shape ofthe coding unit is non-square, the image decoding apparatus 100 maydetermine the ratio of the width and height in the block shapeinformation of the coding unit to be at least one of 1:2, 2:1, 1:4, 4:1,1:8, or 8:1. Also, the image decoding apparatus 100 may determinewhether the coding unit is in a horizontal direction or a verticaldirection, based on the length of the width and the length of the heightof the coding unit. Also, the image decoding apparatus 100 may determinethe size of the coding unit, based on at least one of the length of thewidth, the length of the height, or the area of the coding unit.

According to an embodiment, the image decoding apparatus 100 maydetermine the shape of the coding unit by using the block shapeinformation, and may determine a splitting method of the coding unit byusing the split shape mode information. That is, a coding unit splittingmethod indicated by the split shape mode information may be determinedbased on a block shape indicated by the block shape information used bythe image decoding apparatus 100.

The image decoding apparatus 100 may obtain the split shape modeinformation from a bitstream. However, an embodiment is not limitedthereto, and the image decoding apparatus 100 and the image encodingapparatus 150 may obtain pre-agreed split shape mode information, basedon the block shape information. The image decoding apparatus 100 mayobtain the pre-agreed split shape mode information with respect to alargest coding unit or a smallest coding unit. For example, the imagedecoding apparatus 100 may determine split shape mode information withrespect to the largest coding unit to be a quad split. Also, the imagedecoding apparatus 100 may determine split shape mode informationregarding the smallest coding unit to be “not to perform splitting”. Inparticular, the image decoding apparatus 100 may determine the size ofthe largest coding unit to be 256×256. The image decoding apparatus 100may determine the pre-agreed split shape mode information to be a quadsplit. The quad split is a split shape mode in which both the width andthe height of the coding unit are bisected. The image decoding apparatus100 may obtain a coding unit of a 128×128 size from the largest codingunit of a 256×256 size, based on the split shape mode information. Also,the image decoding apparatus 100 may determine the size of the smallestcoding unit to be 4×4. The image decoding apparatus 100 may obtain splitshape mode information indicating “not to perform splitting” withrespect to the smallest coding unit.

According to an embodiment, the image decoding apparatus 100 may use theblock shape information indicating that the current coding unit has asquare shape. For example, the image decoding apparatus 100 maydetermine whether not to split a square coding unit, whether tovertically split the square coding unit, whether to horizontally splitthe square coding unit, or whether to split the square coding unit intofour coding units, based on the split shape mode information. Referringto FIG. 3 , when the block shape information of a current coding unit300 indicates a square shape, an image decoder 110 may not split acoding unit 310 a having the same size as the current coding unit 300,based on the split shape mode information indicating not to performsplitting, or may determine coding units 310 b, 310 c, or 310 d splitbased on the split shape mode information indicating a preset splittingmethod.

Referring to FIG. 3 , according to an embodiment, the image decodingapparatus 100 may determine two coding units 310 b obtained by splittingthe current coding unit 300 in a vertical direction, based on the splitshape mode information indicating to perform splitting in a verticaldirection. The image decoding apparatus 100 may determine two codingunits 310 c obtained by splitting the current coding unit 300 in ahorizontal direction, based on the split shape mode informationindicating to perform splitting in a horizontal direction. The imagedecoding apparatus 100 may determine four coding units 310 d obtained bysplitting the current coding unit 300 in vertical and horizontaldirections, based on the split shape mode information indicating toperform splitting in vertical and horizontal directions. According to anembodiment, the image decoding apparatus 100 may determine three codingunits 310 e obtained by splitting the current coding unit 300 in avertical direction, based on the split shape mode information indicatingto perform tri (or ternary)-splitting in a vertical direction. The imagedecoding apparatus 100 may determine three coding units 310 f obtainedby splitting the current coding unit 300 in a horizontal direction,based on the split shape mode information indicating to performternary-splitting in a horizontal direction.

However, splitting methods of the square coding unit are not limited tothe aforementioned methods, and may include various methods that may beindicated by the split shape mode information. Preset splitting methodsof splitting the square coding unit will be described in detail below inrelation to various embodiments.

FIG. 4 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a non-squarecoding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may useblock shape information indicating that a current coding unit has anon-square shape. The image decoding apparatus 100 may determine whethernot to split the non-square current coding unit or whether to split thenon-square current coding unit by using a preset splitting method, basedon split shape mode information. Referring to FIG. 4 , when the blockshape information of a current coding unit 400 or 450 indicates anon-square shape, the image decoding apparatus 100 may determine that acoding unit 410 or 460 having the same size as the current coding unit400 or 450, based on the split shape mode information indicating not toperform splitting, or may determine coding units 420 a and 420 b, 430 a,430 b, and 430 c, 470 a and 470 b, or 480 a, 480 b, and 480 c which aresplit based on the split shape mode information indicating a presetsplitting method. Preset splitting methods of splitting a non-squarecoding unit will be described in detail below in relation to variousembodiments.

According to an embodiment, the image decoding apparatus 100 maydetermine a splitting method of a coding unit by using the split shapemode information and, in this case, the split shape mode information mayindicate the number of one or more coding units generated by splitting acoding unit. Referring to FIG. 4 , when the split shape mode informationindicates to split the current coding unit 400 or 450 into two codingunits, the image decoding apparatus 100 may determine two coding units420 a and 420 b, or 470 a and 470 b included in the current coding unit400 or 450, by splitting the current coding unit 400 or 450 based on thesplit shape mode information.

According to an embodiment, when the image decoding apparatus 100 splitsthe non-square current coding unit 400 or 450 based on the split shapemode information, the image decoding apparatus 100 may split a currentcoding unit, in consideration of the location of a long side of thenon-square current coding unit 400 or 450. For example, the imagedecoding apparatus 100 may determine a plurality of coding units bysplitting the current coding unit 400 or 450 by splitting a long side ofthe current coding unit 400 or 450, in consideration of the shape of thecurrent coding unit 400 or 450.

According to an embodiment, when the split shape mode informationindicates to split (tri-split) a coding unit into an odd number ofblocks, the image decoding apparatus 100 may determine an odd number ofcoding units included in the current coding unit 400 or 450. Forexample, when the split shape mode information indicates to split thecurrent coding unit 400 or 450 into three coding units, the imagedecoding apparatus 100 may split the current coding unit 400 or 450 intothree coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c.

According to an embodiment, a ratio of the width and height of thecurrent coding unit 400 or 450 may be 4:1 or 1:4. When the ratio of thewidth and height is 4:1, the block shape information may indicate ahorizontal direction because the length of the width is longer than thelength of the height. When the ratio of the width and height is 1:4, theblock shape information may indicate a vertical direction because thelength of the width is shorter than the length of the height. The imagedecoding apparatus 100 may determine to split a current coding unit intothe odd number of blocks, based on the split shape mode information.Also, the image decoding apparatus 100 may determine a split directionof the current coding unit 400 or 450, based on the block shapeinformation of the current coding unit 400 or 450. For example, when thecurrent coding unit 400 is in the vertical direction, the image decodingapparatus 100 may determine the coding units 430 a, 430 b, and 430 c bysplitting the current coding unit 400 in the horizontal direction. Also,when the current coding unit 450 is in the horizontal direction, theimage decoding apparatus 100 may determine the coding units 480 a, 480b, and 480 c by splitting the current coding unit 450 in the verticaldirection.

According to an embodiment, the image decoding apparatus 100 maydetermine the odd number of coding units included in the current codingunit 400 or 450, and not all the determined coding units may have thesame size. For example, a preset coding unit 430 b or 480 b from amongthe determined odd number of coding units 430 a, 430 b, and 430 c, or480 a, 480 b, and 480 c may have a size different from the size of theother coding units 430 a and 430 c, or 480 a and 480 c. That is, codingunits which may be determined by splitting the current coding unit 400or 450 may have multiple sizes and, in some cases, all of the odd numberof coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c mayhave different sizes.

According to an embodiment, when the split shape mode informationindicates to split a coding unit into the odd number of blocks, theimage decoding apparatus 100 may determine the odd number of codingunits included in the current coding unit 400 or 450, and in addition,may put a preset restriction on at least one coding unit from among theodd number of coding units generated by splitting the current codingunit 400 or 450. Referring to FIG. 4 , the image decoding apparatus 100may allow a decoding process of the coding unit 430 b or 480 b to bedifferent from that of the other coding units 430 a and 430 c, or 480 aor 480 c, wherein coding unit 430 b or 480 b is at a center locationfrom among the three coding units 430 a, 430 b, and 430 c or 480 a, 480b, and 480 c generated by splitting the current coding unit 400 or 450.For example, the image decoding apparatus 100 may restrict the codingunit 430 b or 480 b at the center location to be no longer split or tobe split only a preset number of times, unlike the other coding units430 a and 430 c, or 480 a and 480 c.

FIG. 5 illustrates a process, performed by the image decoding apparatus100, of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split a square first coding unit 500 into coding units,based on at least one of the block shape information and the split shapemode information, or may determine to not split the square first codingunit 500. According to an embodiment, when the split shape modeinformation indicates to split the first coding unit 500 in a horizontaldirection, the image decoding apparatus 100 may determine a secondcoding unit 510 by splitting the first coding unit 500 in a horizontaldirection. A first coding unit, a second coding unit, and a third codingunit used according to an embodiment are terms used to understand arelation before and after splitting a coding unit. For example, thesecond coding unit may be determined by splitting the first coding unit,and the third coding unit may be determined by splitting the secondcoding unit. It will be understood that the structure of the firstcoding unit, the second coding unit, and the third coding unit followsthe above descriptions.

According to an embodiment, the image decoding apparatus 100 maydetermine to split the determined second coding unit 510 into codingunits, based on at least one of the block shape information and thesplit shape mode information, or may determine to not split thedetermined second coding unit 510. Referring to FIG. 5 , the imagedecoding apparatus 100 may split the non-square second coding unit 510,which is determined by splitting the first coding unit 500, into one ormore third coding units 520 a, or 520 b, 520 c, and 520 d at least oneof the block shape information and the split shape mode information, ormay not split the non-square second coding unit 510. The image decodingapparatus 100 may obtain at least one of the block shape information andthe split shape mode information, and may split a plurality ofvarious-shaped second coding units (e.g., 510) by splitting the firstcoding unit 500, based on at least one of the obtained block shapeinformation and the obtained split shape mode information, and thesecond coding unit 510 may be split by using a splitting method of thefirst coding unit 500 based on at least one of the block shapeinformation and the split shape mode information. According to anembodiment, when the first coding unit 500 is split into the secondcoding units 510 based on at least one of block shape information andsplit shape mode information about the first coding unit 500, the secondcoding unit 510 may also be split into the third coding units 520 a, or520 b, 520 c, and 520 d based on at least one of block shape informationand split shape mode information about the second coding unit 510. Thatis, a coding unit may be recursively split based on at least one ofblock shape information and split shape mode information about eachcoding unit. Therefore, a square coding unit may be determined bysplitting a non-square coding unit, and a non-square coding unit may bedetermined by recursively splitting the square coding unit.

Referring to FIG. 5 , a preset coding unit (e.g., a coding unit locatedat a center location or a square coding unit) from among the odd numberof third coding units 520 b, 520 c, and 520 d determined by splittingthe non-square second coding unit 510 may be recursively split.According to an embodiment, the non-square third coding unit 520 b fromamong the odd number of third coding units 520 b, 520 c, and 520 d maybe split in a horizontal direction into a plurality of fourth codingunits. A non-square fourth coding unit 530 b or 530 d from among aplurality of fourth coding units 530 a, 530 b, 530 c, and 530 d may bere-split into a plurality of coding units. For example, the non-squarefourth coding unit 530 b or 530 d may be re-split into the odd number ofcoding units. A method that may be used to recursively split a codingunit will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may spliteach of the third coding units 520 a, or 520 b, 520 c, and 520 d intocoding units, based on at least one of block shape information and splitshape mode information. Also, the image decoding apparatus 100 maydetermine not to split the second coding unit 510 based on at least oneof block shape information and split shape mode information. Accordingto an embodiment, the image decoding apparatus 100 may split thenon-square second coding unit 510 into the odd number of third codingunits 520 b, 520 c, and 520 d. The image decoding apparatus 100 may puta preset restriction on a preset third coding unit from among the oddnumber of third coding units 520 b, 520 c, and 520 d. For example, theimage decoding apparatus 100 may restrict the third coding unit 520 c ata center location from among the odd number of third coding units 520 b,520 c, and 520 d to be no longer split or to be split a settable numberof times.

Referring to FIG. 5 , the image decoding apparatus 100 may restrict thethird coding unit 520 c, which is at the center location from among theodd number of third coding units 520 b, 520 c, and 520 d included in thenon-square second coding unit 510, to be no longer split, to be split byusing a preset splitting method (e.g., split into only four coding unitsor split by using a splitting method of the second coding unit 510), orto be split only a preset number of times (e.g., split only n times(where n>0)). However, the restrictions on the third coding unit 520 cat the center location are not limited to the aforementioned examples,and it should be interpreted that the restrictions may include variousrestrictions for decoding the third coding unit 520 c at the centerlocation differently from the other third coding units 520 b and 520 d.

According to an embodiment, the image decoding apparatus 100 may obtainat least one of block shape information and split shape modeinformation, which is used to split a current coding unit, from a presetlocation in the current coding unit.

FIG. 6 illustrates a method, performed by the image decoding apparatus100, of determining a preset coding unit from among an odd number ofcoding units, according to an embodiment.

Referring to FIG. 6 , at least one of block shape information and splitshape mode information about a current coding unit 600 or 650 may beobtained from a sample of a preset location (e.g., a sample 640 or 690of a center location) from among a plurality of samples included in thecurrent coding unit 600 or 650. However, the preset location in thecurrent coding unit 600, from which at least one of the block shapeinformation and the split shape mode information may be obtained, is notlimited to the center location in FIG. 6 , and may include variouslocations included in the current coding unit 600 (e.g., top, bottom,left, right, upper-left, lower-left, upper-right, and lower-rightlocations). The image decoding apparatus 100 may obtain at least one ofthe block shape information and the split shape mode information fromthe preset location and may determine to split or not to split thecurrent coding unit into various-shaped and various-sized coding units.

According to an embodiment, when the current coding unit is split into apreset number of coding units, the image decoding apparatus 100 mayselect one of the coding units. Various methods may be used to selectone of a plurality of coding units, as will be described below inrelation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit into a plurality of coding units, and maydetermine a coding unit at a preset location.

According to an embodiment, the image decoding apparatus 100 may useinformation indicating locations of the odd number of coding units, soas to determine a coding unit at a center location from among the oddnumber of coding units. Referring to FIG. 6 , the image decodingapparatus 100 may determine the odd number of coding units 620 a, 620 b,and 620 c or the odd number of coding units 660 a, 660 b, and 660 c bysplitting the current coding unit 600 or the current coding unit 650.The image decoding apparatus 100 may determine the middle coding unit620 b or the middle coding unit 660 b by using information about thelocations of the odd number of coding units 620 a, 620 b, and 620 c orthe odd number of coding units 660 a, 660 b, and 660 c. For example, theimage decoding apparatus 100 may determine the coding unit 620 b of thecenter location by determining the locations of the coding units 620 a,620 b, and 620 c based on information indicating locations of presetsamples included in the coding units 620 a, 620 b, and 620 c. In detail,the image decoding apparatus 100 may determine the coding unit 620 b atthe center location by determining the locations of the coding units 620a, 620 b, and 620 c based on information indicating locations oftop-left samples 630 a, 630 b, and 630 c of the coding units 620 a, 620b, and 620 c.

According to an embodiment, the information indicating the locations ofthe top-left samples 630 a, 630 b, and 630 c, which are included in thecoding units 620 a, 620 b, and 620 c, respectively, may includeinformation about locations or coordinates of the coding units 620 a,620 b, and 620 c in a picture. According to an embodiment, theinformation indicating the locations of the top-left samples 630 a, 630b, and 630 c, which are included in the coding units 620 a, 620 b, and620 c, respectively, may include information indicating widths orheights of the coding units 620 a, 620 b, and 620 c included in thecurrent coding unit 600, and the widths or heights may correspond toinformation indicating differences between the coordinates of the codingunits 620 a, 620 b, and 620 c in the picture. That is, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation by directly using the information about the locations orcoordinates of the coding units 620 a, 620 b, and 620 c in the picture,or by using the information about the widths or heights of the codingunits, which correspond to the difference values between thecoordinates.

According to an embodiment, information indicating the location of thetop-left sample 630 a of the upper coding unit 620 a may includecoordinates (xa, ya), information indicating the location of thetop-left sample 630 b of the middle coding unit 620 b may includecoordinates (xb, yb), and information indicating the location of thetop-left sample 630 c of the lower coding unit 620 c may includecoordinates (xc, yc). The image decoding apparatus 100 may determine themiddle coding unit 620 b by using the coordinates of the top-leftsamples 630 a, 630 b, and 630 c which are included in the coding units620 a, 620 b, and 620 c, respectively. For example, when the coordinatesof the top-left samples 630 a, 630 b, and 630 c are sorted in anascending or descending order, the coding unit 620 b including thecoordinates (xb, yb) of the sample 630 b at a center location may bedetermined as a coding unit at a center location from among the codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600. However, the coordinates indicating the locations of thetop-left samples 630 a, 630 b, and 630 c may include coordinatesindicating absolute locations in the picture, or may use coordinates(dxb, dyb) indicating a relative location of the top-left sample 630 bof the middle coding unit 620 b and coordinates (dxc, dyc) indicating arelative location of the top-left sample 630 c of the lower coding unit620 c with reference to the location of the top-left sample 630 a of theupper coding unit 620 a. A method of determining a coding unit at apreset location by using coordinates of a sample included in the codingunit, as information indicating a location of the sample, is not limitedto the aforementioned method, and may include various arithmetic methodscapable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit 600 into a plurality of coding units 620 a, 620b, and 620 c, and may select one of the coding units 620 a, 620 b, and620 c based on a preset criterion. For example, the image decodingapparatus 100 may select the coding unit 620 b, which has a sizedifferent from that of the others, from among the coding units 620 a,620 b, and 620 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width or height of each of the coding units 620 a, 620 b,and 620 c by using the coordinates (xa, ya) that is the informationindicating the location of the top-left sample 630 a of the upper codingunit 620 a, the coordinates (xb, yb) that is the information indicatingthe location of the top-left sample 630 b of the middle coding unit 620b, and the coordinates (xc, yc) that is the information indicating thelocation of the top-left sample 630 c of the lower coding unit 620 c.The image decoding apparatus 100 may determine the respective sizes ofthe coding units 620 a, 620 b, and 620 c by using the coordinates (xa,ya), (xb, yb), and (xc, yc) indicating the locations of the coding units620 a, 620 b, and 620 c. According to an embodiment, the image decodingapparatus 100 may determine the width of the upper coding unit 620 a tobe the width of the current coding unit 600. The image decodingapparatus 100 may determine the height of the upper coding unit 620 a tobe yb-ya. According to an embodiment, the image decoding apparatus 100may determine the width of the middle coding unit 620 b to be the widthof the current coding unit 600. The image decoding apparatus 100 maydetermine the height of the middle coding unit 620 b to be yc-yb.According to an embodiment, the image decoding apparatus 100 maydetermine the width or height of the lower coding unit 620 c by usingthe width or height of the current coding unit 600 or the widths orheights of the upper and middle coding units 620 a and 620 b. The imagedecoding apparatus 100 may determine a coding unit, which has a sizedifferent from that of the others, based on the determined widths andheights of the coding units 620 a, 620 b, and 620 c. Referring to FIG. 6, the image decoding apparatus 100 may determine the middle coding unit620 b, which has a size different from the size of the upper and lowercoding units 620 a and 620 c, as the coding unit of the preset location.However, the aforementioned method, performed by the image decodingapparatus 100, of determining a coding unit having a size different fromthe size of the other coding units merely corresponds to an example ofdetermining a coding unit at a preset location by using the sizes ofcoding units, which are determined based on coordinates of samples, andthus various methods of determining a coding unit at a preset locationby comparing the sizes of coding units, which are determined based oncoordinates of preset samples, may be used.

The image decoding apparatus 100 may determine the width or height ofeach of the coding units 660 a, 660 b, and 660 c by using thecoordinates (xd, yd) that is information indicating the location of atop-left sample 670 a of the left coding unit 660 a, the coordinates(xe, ye) that is information indicating the location of a top-leftsample 670 b of the middle coding unit 660 b, and the coordinates (xf,yf) that is information indicating a location of the top-left sample 670c of the right coding unit 660 c. The image decoding apparatus 100 maydetermine the respective sizes of the coding units 660 a, 660 b, and 660c by using the coordinates (xd, yd), (xe, ye), and (xf, yf) indicatingthe locations of the coding units 660 a, 660 b, and 660 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width of the left coding unit 660 a to be xe-xd. The imagedecoding apparatus 100 may determine the height of the left coding unit660 a to be the height of the current coding unit 650. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe middle coding unit 660 b to be xf-xe. The image decoding apparatus100 may determine the height of the middle coding unit 660 b to be theheight of the current coding unit 650. According to an embodiment, theimage decoding apparatus 100 may determine the width or height of theright coding unit 660 c by using the width or height of the currentcoding unit 650 or the widths or heights of the left and middle codingunits 660 a and 660 b. The image decoding apparatus 100 may determine acoding unit, which has a size different from that of the others, basedon the determined widths and heights of the coding units 660 a, 660 b,and 660 c. Referring to FIG. 6 , the image decoding apparatus 100 maydetermine the middle coding unit 660 b, which has a size different fromthe sizes of the left and right coding units 660 a and 660 c, as thecoding unit of the preset location. However, the aforementioned method,performed by the image decoding apparatus 100, of determining a codingunit having a size different from the size of the other coding unitsmerely corresponds to an example of determining a coding unit at apreset location by using the sizes of coding units, which are determinedbased on coordinates of samples, and thus various methods of determininga coding unit at a preset location by comparing the sizes of codingunits, which are determined based on coordinates of preset samples, maybe used.

However, locations of samples considered to determine locations ofcoding units are not limited to the aforementioned top-left locations,and information about arbitrary locations of samples included in thecoding units may be used.

According to an embodiment, the image decoding apparatus 100 may selecta coding unit at a preset location from among an odd number of codingunits determined by splitting the current coding unit, in considerationof the shape of the current coding unit. For example, when the currentcoding unit has a non-square shape, a width of which is longer than itsheight, the image decoding apparatus 100 may determine the coding unitat the preset location in a horizontal direction. That is, the imagedecoding apparatus 100 may determine one of coding units at differentlocations in a horizontal direction and may put a restriction on thecoding unit. When the current coding unit has a non-square shape, aheight of which is longer than its width, the image decoding apparatus100 may determine the coding unit at the preset location in a verticaldirection. That is, the image decoding apparatus 100 may determine oneof coding units at different locations in a vertical direction and mayput a restriction on the coding unit.

According to an embodiment, the image decoding apparatus 100 may useinformation indicating respective locations of an even number of codingunits, so as to determine the coding unit at the preset location fromamong the even number of coding units. The image decoding apparatus 100may determine an even number of coding units by splitting (binary or bisplitting) the current coding unit, and may determine the coding unit atthe preset location by using the information about the locations of theeven number of coding units. An operation related thereto may correspondto the operation of determining a coding unit at a preset location(e.g., a center location) from among an odd number of coding units,which is described in detail above with reference to FIG. 6 , and thusdetailed descriptions thereof are not provided here.

According to an embodiment, when a non-square current coding unit issplit into a plurality of coding units, preset information about acoding unit at a preset location may be used in a splitting process todetermine the coding unit at the preset location from among theplurality of coding units. For example, the image decoding apparatus 100may use at least one of block shape information and split shape modeinformation, which is stored in a sample included in a middle codingunit, in a splitting process to determine a coding unit at a centerlocation from among the plurality of coding units determined bysplitting the current coding unit.

Referring to FIG. 6 , the image decoding apparatus 100 may split thecurrent coding unit 600 into the plurality of coding units 620 a, 620 b,and 620 c based on at least one of the block shape information and thesplit shape mode information, and may determine the coding unit 620 b ata center location from among the plurality of the coding units 620 a,620 b, and 620 c. Furthermore, the image decoding apparatus 100 maydetermine the coding unit 620 b at the center location, in considerationof a location from which based on at least one of the block shapeinformation and the split shape mode information is obtained. That is,at least one of block shape information and split shape mode informationabout the current coding unit 600 may be obtained from the sample 640 ata center location of the current coding unit 600 and, when the currentcoding unit 600 is split into the plurality of coding units 620 a, 620b, and 620 c based on at least one of the block shape information andthe split shape mode information, the coding unit 620 b including thesample 640 may be determined as the coding unit at the center location.However, information used to determine the coding unit at the centerlocation is not limited to at least one of block shape information andsplit shape mode information, and various types of information may beused to determine the coding unit at the center location.

According to an embodiment, preset information for identifying thecoding unit at the preset location may be obtained from a preset sampleincluded in a coding unit to be determined. Referring to FIG. 6 , theimage decoding apparatus 100 may use at least one of the block shapeinformation and the split shape mode information, which is obtained froma sample at a preset location in the current coding unit 600 (e.g., asample at a center location of the current coding unit 600), todetermine a coding unit at a preset location from among the plurality ofthe coding units 620 a, 620 b, and 620 c determined by splitting thecurrent coding unit 600 (e.g., a coding unit at a center location fromamong a plurality of split coding units). That is, the image decodingapparatus 100 may determine the sample at the preset location byconsidering a block shape of the current coding unit 600, may determinethe coding unit 620 b including a sample, from which preset information(e.g., at least one of the block shape information and the split shapemode information) is obtainable, from among the plurality of codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600, and may put a preset restriction on the coding unit 620 b.Referring to FIG. 6 , according to an embodiment, the image decodingapparatus 100 may determine the sample 640 at the center location of thecurrent coding unit 600 as the sample from which the preset informationis obtainable, and may put a preset restriction on the coding unit 620 bincluding the sample 640, in a decoding operation. However, the locationof the sample from which the preset information is obtainable is notlimited to the aforementioned location, and may include arbitrarylocations of samples included in the coding unit 620 b to be determinedfor a restriction.

According to an embodiment, the location of the sample from which thepreset information is obtainable may be determined based on the shape ofthe current coding unit 600. According to an embodiment, the block shapeinformation may indicate whether the current coding unit has a square ornon-square shape, and the location of the sample from which the presetinformation is obtainable may be determined based on the shape. Forexample, the image decoding apparatus 100 may determine a sample locatedon a boundary for splitting at least one of a width and height of thecurrent coding unit in half, as the sample from which the presetinformation is obtainable, by using at least one of information aboutthe width of the current coding unit and information about the height ofthe current coding unit. As another example, when the block shapeinformation of the current coding unit indicates a non-square shape, theimage decoding apparatus 100 may determine one of samples adjacent to aboundary for splitting a long side of the current coding unit in half,as the sample from which the preset information is obtainable.

According to an embodiment, when the current coding unit is split into aplurality of coding units, the image decoding apparatus 100 may use atleast one of the block shape information and the split shape modeinformation so as to determine a coding unit at a preset location fromamong the plurality of coding units. According to an embodiment, theimage decoding apparatus 100 may obtain at least one of the block shapeinformation and the split shape mode information from a sample at apreset location in a coding unit, and may split the plurality of codingunits, which are generated by splitting the current coding unit, byusing at least one of the block shape information and the split shapemode information, which is obtained from the sample of the presetlocation in each of the plurality of coding units. That is, a codingunit may be recursively split based on at least one of the block shapeinformation and the split shape mode information, which is obtained fromthe sample at the preset location in each coding unit. An operation ofrecursively splitting a coding unit is described above with reference toFIG. 5 , and thus detailed descriptions thereof are not provided here.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more coding units by splitting the current coding unit,and may determine an order of decoding the one or more coding units,based on a preset block (e.g., the current coding unit).

FIG. 7 illustrates an order of processing a plurality of coding unitswhen the image decoding apparatus 100 determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 710 a and 710 b by splitting a firstcoding unit 700 in a vertical direction, may determine second codingunits 730 a and 730 b by splitting the first coding unit 700 in ahorizontal direction, or may determine second coding units 750 a to 750d by splitting the first coding unit 700 in vertical and horizontaldirections, based on at least one of block shape information and splitshape mode information.

Referring to FIG. 7 , the image decoding apparatus 100 may determine toprocess the second coding units 710 a and 710 b in a horizontaldirection order 710 c, the second coding units 710 a and 710 b beingdetermined by splitting the first coding unit 700 in a verticaldirection. The image decoding apparatus 100 may determine to process thesecond coding units 730 a and 730 b in a vertical direction order 730 c,the second coding units 730 a and 730 b being determined by splittingthe first coding unit 700 in a horizontal direction. The image decodingapparatus 100 may determine the second coding units 750 a, 750 b, 750 c,and 750 d, which are determined by splitting the first coding unit 700in vertical and horizontal directions, according to a preset order(e.g., in a raster scan order or Z-scan order 750 e) by which codingunits in a row are processed and then coding units in a next row areprocessed.

According to an embodiment, the image decoding apparatus 100 mayrecursively split coding units. Referring to FIG. 7 , the image decodingapparatus 100 may determine the plurality of coding units 710 a and 710b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750 d by splitting thefirst coding unit 700, and may recursively split each of the determinedplurality of coding units 710 a and 710 b, 730 a and 730 b, or 750 a,750 b, 750 c, and 750 d. A splitting method of the plurality of codingunits 710 a and 710 b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750d may correspond to a splitting method of the first coding unit 700.Accordingly, each of the plurality of coding units 710 a and 710 b, 730a and 730 b, or 750 a, 750 b, 750 c, and 750 d may be independentlysplit into a plurality of coding units. Referring to FIG. 7 , the imagedecoding apparatus 100 may determine the second coding units 710 a and710 b by splitting the first coding unit 700 in a vertical direction,and may determine to independently split each of the second coding units710 a and 710 b or not to split the second coding units 710 a and 710 b.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 720 a and 720 b by splitting the leftsecond coding unit 710 a in a horizontal direction, and may not splitthe right second coding unit 710 b.

According to an embodiment, a processing order of coding units may bedetermined based on an operation of splitting a coding unit. In otherwords, a processing order of split coding units may be determined basedon a processing order of coding units immediately before being split.The image decoding apparatus 100 may determine a processing order of thethird coding units 720 a and 720 b determined by splitting the leftsecond coding unit 710 a, independently of the right second coding unit710 b. Because the third coding units 720 a and 720 b are determined bysplitting the left second coding unit 710 a in a horizontal direction,the third coding units 720 a and 720 b may be processed in a verticaldirection order 720 c. Because the left and right second coding units710 a and 710 b are processed in the horizontal direction order 710 c,the right second coding unit 710 b may be processed after the thirdcoding units 720 a and 720 b included in the left second coding unit 710a are processed in the vertical direction order 720 c. It should beconstrued that an operation of determining a processing order of codingunits based on a coding unit before being split is not limited to theaforementioned example, and various methods may be used to independentlyprocess coding units, which are split and determined to various shapes,in a preset order.

FIG. 8 illustrates a process, performed by the image decoding apparatus100, of determining that a current coding unit is to be split into anodd number of coding units, when the coding units are not processable ina preset order, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine that the current coding unit is to be split into an odd numberof coding units, based on obtained block shape information and splitshape mode information. Referring to FIG. 8 , a square first coding unit800 may be split into non-square second coding units 810 a and 810 b,and the second coding units 810 a and 810 b may be independently splitinto third coding units 820 a and 820 b, and 820 c, 820 d, and 820 e.According to an embodiment, the image decoding apparatus 100 maydetermine the plurality of third coding units 820 a and 820 b bysplitting the left second coding unit 810 a in a horizontal direction,and may split the right second coding unit 810 b into the odd number ofthird coding units 820 c, 820 d, and 820 e.

According to an embodiment, the image decoding apparatus 100 maydetermine whether there are an odd number of split coding units, bydetermining whether the third coding units 820 a and 820 b, and 820 c,820 d, and 820 e are processable in a preset order. Referring to FIG. 8, the image decoding apparatus 100 may determine the third coding units820 a and 820 b, and 820 c, 820 d, and 820 e by recursively splittingthe first coding unit 800. The image decoding apparatus 100 maydetermine whether any of the first coding unit 800, the second codingunits 810 a and 810 b, or the third coding units 820 a and 820 b, and820 c, 820 d, and 820 e is to be split into an odd number of codingunits, based on at least one of the block shape information and thesplit shape mode information. For example, the second coding unit 810 blocated in the right from among the second coding units 810 a and 810 bmay be split into an odd number of third coding units 820 c, 820 d, and820 e. A processing order of a plurality of coding units included in thefirst coding unit 800 may be a preset order (e.g., a Z-scan order 830),and the image decoding apparatus 100 may determine whether the thirdcoding units 820 c, 820 d, and 820 e, which are determined by splittingthe right second coding unit 810 b into an odd number of coding units,satisfy a condition for processing in the preset order.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the third coding units 820 a and 820 b, and 820 c, 820d, and 820 e included in the first coding unit 800 satisfy the conditionfor processing in the preset order, and the condition relates to whetherat least one of a width and height of the second coding units 810 a and810 b is to be split in half along a boundary of the third coding units820 a and 820 b, and 820 c, 820 d, and 820 e. For example, the thirdcoding units 820 a and 820 b determined when the height of the leftsecond coding unit 810 a of the non-square shape is split in half maysatisfy the condition. It may be determined that the third coding units820 c, 820 d, and 820 e do not satisfy the condition because theboundaries of the third coding units 820 c, 820 d, and 820 e determinedwhen the right second coding unit 810 b is split into three coding unitsare unable to split the width or height of the right second coding unit810 b in half. When the condition is not satisfied as described above,the image decoding apparatus 100 may determine disconnection of a scanorder, and may determine that the right second coding unit 810 b is tobe split into an odd number of coding units, based on a result of thedetermination. According to an embodiment, when a coding unit is splitinto an odd number of coding units, the image decoding apparatus 100 mayput a preset restriction on a coding unit at a preset location fromamong the split coding units. The restriction or the preset location isdescribed above in relation to various embodiments, and thus detaileddescriptions thereof are not provided herein.

FIG. 9 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a first codingunit 900, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may splitthe first coding unit 900, based on at least one of block shapeinformation and split shape mode information that is obtained through areceiver (not shown). The square first coding unit 900 may be split intofour square coding units, or may be split into a plurality of non-squarecoding units. For example, referring to FIG. 9 , when the block shapeinformation indicates that the first coding unit 900 is a square and thesplit shape mode information indicates to split the first coding unit900 into non-square coding units, the image decoding apparatus 100 maysplit the first coding unit 900 into a plurality of non-square codingunits. In detail, when the split shape mode information indicates todetermine an odd number of coding units by splitting the first codingunit 900 in a horizontal direction or a vertical direction, the imagedecoding apparatus 100 may split the square first coding unit 900 intoan odd number of coding units, e.g., second coding units 910 a, 910 b,and 910 c determined by splitting the square first coding unit 900 in avertical direction or second coding units 920 a, 920 b, and 920 cdetermined by splitting the square first coding unit 900 in a horizontaldirection.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the second coding units 910 a, 910 b, 910 c, 920 a,920 b, and 920 c included in the first coding unit 900 satisfy acondition for processing in a preset order, and the condition relates towhether at least one of a width and height of the first coding unit 900is to be split in half along a boundary of the second coding units 910a, 910 b, 910 c, 920 a, 920 b, and 920 c. Referring to FIG. 9 , becauseboundaries of the second coding units 910 a, 910 b, and 910 c determinedby splitting the square first coding unit 900 in a vertical direction donot split the width of the first coding unit 900 in half, it may bedetermined that the first coding unit 900 does not satisfy the conditionfor processing in the preset order. In addition, because boundaries ofthe second coding units 920 a, 920 b, and 920 c determined by splittingthe square first coding unit 900 in a horizontal direction do not splitthe height of the first coding unit 900 in half, it may be determinedthat the first coding unit 900 does not satisfy the condition forprocessing in the preset order. When the condition is not satisfied asdescribed above, the image decoding apparatus 100 may determinedisconnection of a scan order, and may determine that the first codingunit 900 is to be split into an odd number of coding units, based on aresult of the determination. According to an embodiment, when a codingunit is split into an odd number of coding units, the image decodingapparatus 100 may put a preset restriction on a coding unit at a presetlocation from among the split coding units. The restriction or thepreset location is described above in relation to various embodiments,and thus detailed descriptions thereof are not provided herein.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shaped coding units by splitting a first coding unit.

Referring to FIG. 9 , the image decoding apparatus 100 may split thesquare first coding unit 900 or a non-square first coding unit 930 or950 into various-shaped coding units.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined as the image decoding apparatus 100 splits afirst coding unit 1000, satisfies a preset condition, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split the square first coding unit 1000 into non-squaresecond coding units 1010 a and 1010 b or 1020 a and 1020 b, based on atleast one of block shape information and split shape mode informationwhich is obtained by the receiver (not shown). The second coding units1010 a and 1010 b or 1020 a and 1020 b may be independently split.Accordingly, the image decoding apparatus 100 may determine to split ornot to split each of the second coding units 1010 a and 1010 b or 1020 aand 1020 b into a plurality of coding units, based on at least one ofblock shape information and split shape mode information about each ofthe second coding units 1010 a and 1010 b or 1020 a and 1020 b.According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 1012 a and 1012 b by splitting thenon-square left second coding unit 1010 a, which is determined bysplitting the first coding unit 1000 in a vertical direction, in ahorizontal direction. However, when the left second coding unit 1010 ais split in a horizontal direction, the image decoding apparatus 100 mayrestrict the right second coding unit 1010 b to not be split in ahorizontal direction in which the left second coding unit 1010 a issplit. When third coding units 1014 a and 1014 b are determined bysplitting the right second coding unit 1010 b in a same direction,because the left second coding unit 1010 a and the right second codingunit 1010 b are independently split in a horizontal direction, the thirdcoding units 1012 a and 1012 b or 1014 a and 1014 b may be determined.However, this case serves equally as a case in which the image decodingapparatus 100 splits the first coding unit 1000 into four square secondcoding units 1030 a, 1030 b, 1030 c, and 1030 d, based on at least oneof the block shape information and the split shape mode information, andmay be inefficient in terms of image decoding.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 1022 a and 1022 b or 1024 a and 1024 b bysplitting the non-square second coding unit 1020 a or 1020 b, which isdetermined by splitting the first coding unit 1000 in a horizontaldirection, in a vertical direction. However, when a second coding unit(e.g., the upper second coding unit 1020 a) is split in a verticaldirection, for the aforementioned reason, the image decoding apparatus100 may restrict the other second coding unit (e.g., the lower secondcoding unit 1020 b) to not be split in a vertical direction in which theupper second coding unit 1020 a is split.

FIG. 11 illustrates a process, performed by the image decoding apparatus100, of splitting a square coding unit when split shape mode informationindicates that the square coding unit is to not be split into foursquare coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 1110 a and 1110 b or 1120 a and 1120 b,etc. by splitting a first coding unit 1100, based on at least one ofblock shape information and split shape mode information. The splitshape mode information may include information about various methods ofsplitting a coding unit, but the information about various splittingmethods may not include information for splitting a coding unit intofour square coding units. Based on the split shape mode information, theimage decoding apparatus 100 does not split the square first coding unit1100 into four square second coding units 1130 a, 1130 b, 1130 c, and1130 d. The image decoding apparatus 100 may determine the non-squaresecond coding units 1110 a and 1110 b or 1120 a and 1120 b, etc., basedon the split shape mode information.

According to an embodiment, the image decoding apparatus 100 mayindependently split the non-square second coding units 1110 a and 1110 bor 1120 a and 1120 b, etc. Each of the second coding units 1110 a and1110 b or 1120 a and 1120 b, etc. may be recursively split in a presetorder, and this splitting method may correspond to a method of splittingthe first coding unit 1100, based on at least one of the block shapeinformation and the split shape mode information.

For example, the image decoding apparatus 100 may determine square thirdcoding units 1112 a and 1112 b by splitting the left second coding unit1110 a in a horizontal direction, and may determine square third codingunits 1114 a and 1114 b by splitting the right second coding unit 1110 bin a horizontal direction. Furthermore, the image decoding apparatus 100may determine square third coding units 1116 a, 1116 b, 1116 c, and 1116d by splitting both the left second coding unit 1110 a and the rightsecond coding unit 1110 b in a horizontal direction. In this case,coding units having the same shape as the four square second codingunits 1130 a, 1130 b, 1130 c, and 1130 d split from the first codingunit 1100 may be determined.

As another example, the image decoding apparatus 100 may determinesquare third coding units 1122 a and 1122 b by splitting the uppersecond coding unit 1120 a in a vertical direction, and may determinesquare third coding units 1124 a and 1124 b by splitting the lowersecond coding unit 1120 b in a vertical direction. Furthermore, theimage decoding apparatus 100 may determine square third coding units1126 a, 1126 b, 1126 c, and 1126 d by splitting both the upper secondcoding unit 1120 a and the lower second coding unit 1120 b in a verticaldirection. In this case, coding units having the same shape as the foursquare second coding units 1130 a, 1130 b, 1130 c, and 1130 d split fromthe first coding unit 1100 may be determined.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may split afirst coding unit 1200, based on at least one of block shape informationand split shape mode information. When the block shape informationindicates a square shape and the split shape mode information indicatesto split the first coding unit 1200 in at least one of horizontal andvertical directions, the image decoding apparatus 100 may determinesecond coding units 1210 a and 1210 b or 1220 a and 1220 b, etc. bysplitting the first coding unit 1200. Referring to FIG. 12 , thenon-square second coding units 1210 a and 1210 b or 1220 a and 1220 bdetermined by splitting the first coding unit 1200 in only a horizontaldirection or vertical direction may be independently split based on atleast one of block shape information and split shape mode informationabout each coding unit. For example, the image decoding apparatus 100may determine third coding units 1216 a, 1216 b, 1216 c, and 1216 d bysplitting the second coding units 1210 a and 1210 b, which are generatedby splitting the first coding unit 1200 in a vertical direction, in ahorizontal direction, and may determine third coding units 1226 a, 1226b, 1226 c, and 1226 d by splitting the second coding units 1220 a and1220 b, which are generated by splitting the first coding unit 1200 in ahorizontal direction, in a vertical direction. An operation of splittingthe second coding units 1210 a and 1210 b or 1220 a and 1220 b isdescribed above with reference to FIG. 11 , and thus detaileddescriptions thereof are not provided herein.

According to an embodiment, the image decoding apparatus 100 may processcoding units in a preset order. An operation of processing coding unitsin a preset order is described above with reference to FIG. 7 , and thusdetailed descriptions thereof are not provided herein. Referring to FIG.12 , the image decoding apparatus 100 may determine four square thirdcoding units 1216 a, 1216 b, 1216 c, and 1216 d, and 1226 a, 1226 b,1226 c, and 1226 d by splitting the square first coding unit 1200.According to an embodiment, the image decoding apparatus 100 maydetermine processing orders of the third coding units 1216 a, 1216 b,1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d, based on asplit shape by which the first coding unit 1200 is split.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1216 a, 1216 b, 1216 c, and 1216 d bysplitting the second coding units 1210 a and 1210 b generated bysplitting the first coding unit 1200 in a vertical direction, in ahorizontal direction, and may process the third coding units 1216 a,1216 b, 1216 c, and 1216 d in a processing order 1217 for initiallyprocessing the third coding units 1216 a and 1216 c, which are includedin the left second coding unit 1210 a, in a vertical direction and thenprocessing the third coding unit 1216 b and 1216 d, which are includedin the right second coding unit 1210 b, in a vertical direction.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b generated bysplitting the first coding unit 1200 in a horizontal direction, in avertical direction, and may process the third coding units 1226 a, 1226b, 1226 c, and 1226 d in a processing order 1227 for initiallyprocessing the third coding units 1226 a and 1226 b, which are includedin the upper second coding unit 1220 a, in a horizontal direction andthen processing the third coding unit 1226 c and 1226 d, which areincluded in the lower second coding unit 1220 b, in a horizontaldirection.

Referring to FIG. 12 , the square third coding units 1216 a, 1216 b,1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d may bedetermined by splitting the second coding units 1210 a and 1210 b, and1220 a and 1220 b, respectively. Although the second coding units 1210 aand 1210 b are determined by splitting the first coding unit 1200 in avertical direction differently from the second coding units 1220 a and1220 b which are determined by splitting the first coding unit 1200 in ahorizontal direction, the third coding units 1216 a, 1216 b, 1216 c, and1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d split therefromeventually show same-shaped coding units split from the first codingunit 1200. Accordingly, by recursively splitting a coding unit indifferent manners based on at least one of block shape information andsplit shape mode information, the image decoding apparatus 100 mayprocess a plurality of coding units in different orders even when thecoding units are eventually determined to have the same shape.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine the depth of the coding unit, based on a preset criterion. Forexample, the preset criterion may be the length of a long side of thecoding unit. When the length of a long side of a coding unit beforebeing split is 2n times (n>0) the length of a long side of a splitcurrent coding unit, the image decoding apparatus 100 may determine thata depth of the current coding unit is increased from a depth of thecoding unit before being split, by n. In the following descriptions, acoding unit having an increased depth is expressed as a coding unit of adeeper depth.

Referring to FIG. 13 , according to an embodiment, the image decodingapparatus 100 may determine a second coding unit 1302 and a third codingunit 1304 of deeper depths by splitting a square first coding unit 1300based on block shape information indicating a square shape (for example,the block shape information may be expressed as ‘0: SQUARE’). Assumingthat the size of the square first coding unit 1300 is 2N×2N, the secondcoding unit 1302 determined by splitting a width and height of the firstcoding unit 1300 in ½ may have a size of N×N. Furthermore, the thirdcoding unit 1304 determined by splitting a width and height of thesecond coding unit 1302 in ½ may have a size of N/2×N/2. In this case, awidth and height of the third coding unit 1304 are ¼ times those of thefirst coding unit 1300. When a depth of the first coding unit 1300 is D,a depth of the second coding unit 1302, the width and height of whichare ½ times those of the first coding unit 1300, may be D+1, and a depthof the third coding unit 1304, the width and height of which are ¼ timesthose of the first coding unit 1300, may be D+2.

According to an embodiment, the image decoding apparatus 100 maydetermine a second coding unit 1312 or 1322 and a third coding unit 1314or 1324 of deeper depths by splitting a non-square first coding unit1310 or 1320 based on block shape information indicating a non-squareshape (for example, the block shape information may be expressed as ‘1:NS_VER’ indicating a non-square shape, a height of which is longer thanits width, or as ‘2: NS_HOR’ indicating a non-square shape, a width ofwhich is longer than a height).

The image decoding apparatus 100 may determine a second coding unit1302, 1312, or 1322 by splitting at least one of a width and height ofthe first coding unit 1310 having a size of N×2N. That is, the imagedecoding apparatus 100 may determine the second coding unit 1302 havinga size of N×N or the second coding unit 1322 having a size of N×N/2 bysplitting the first coding unit 1310 in a horizontal direction, or maydetermine the second coding unit 1312 having a size of N/2×N bysplitting the first coding unit 1310 in horizontal and verticaldirections.

According to an embodiment, the image decoding apparatus 100 maydetermine the second coding unit 1302, 1312, or 1322 by splitting atleast one of a width and height of the first coding unit 1320 having asize of 2N×N. That is, the image decoding apparatus 100 may determinethe second coding unit 1302 having a size of N×N or the second codingunit 1312 having a size of N/2×N by splitting the first coding unit 1320in a vertical direction, or may determine the second coding unit 1322having a size of N×N/2 by splitting the first coding unit 1320 inhorizontal and vertical directions.

According to an embodiment, the image decoding apparatus 100 maydetermine a third coding unit 1304, 1314, or 1324 by splitting at leastone of a width and height of the second coding unit 1302 having a sizeof N×N. That is, the image decoding apparatus 100 may determine thethird coding unit 1304 having a size of N/2×N/2, the third coding unit1314 having a size of N/4×N/2, or the third coding unit 1324 having asize of N/2×N/4 by splitting the second coding unit 1302 in vertical andhorizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1312 having asize of N/2×N. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1324 having a size of N/2×N/4 by splitting the second coding unit1312 in a horizontal direction, or may determine the third coding unit1314 having a size of N/4×N/2 by splitting the second coding unit 1312in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1322 having asize of N×N/2. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1314 having a size of N/4×N/2 by splitting the second coding unit1322 in a vertical direction, or may determine the third coding unit1324 having a size of N/2×N/4 by splitting the second coding unit 1322in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 may splitthe square coding unit 1300, 1302, or 1304 in a horizontal or verticaldirection. For example, the image decoding apparatus 100 may determinethe first coding unit 1310 having a size of N×2N by splitting the firstcoding unit 1300 having a size of 2N×2N in a vertical direction, or maydetermine the first coding unit 1320 having a size of 2N×N by splittingthe first coding unit 1300 in a horizontal direction. According to anembodiment, when a depth is determined based on the length of thelongest side of a coding unit, a depth of a coding unit determined bysplitting the first coding unit 1300 having a size of 2N×2N in ahorizontal or vertical direction may be the same as the depth of thefirst coding unit 1300.

According to an embodiment, a width and height of the third coding unit1314 or 1324 may be ¼ times those of the first coding unit 1310 or 1320.When a depth of the first coding unit 1310 or 1320 is D, a depth of thesecond coding unit 1312 or 1322, the width and height of which are ½times those of the first coding unit 1310 or 1320, may be D+1, and adepth of the third coding unit 1314 or 1324, the width and height ofwhich are ¼ times those of the first coding unit 1310 or 1320, may beD+2.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shape second coding units by splitting a square firstcoding unit 1400. Referring to FIG. 14 , the image decoding apparatus100 may determine second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d by splitting the first codingunit 1400 in at least one of vertical and horizontal directions based onsplit shape mode information. That is, the image decoding apparatus 100may determine the second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d, based on the split shape modeinformation of the first coding unit 1400.

According to an embodiment, depths of the second coding units 1402 a and1402 b, 1404 a and 1404 b, and 1406 a, 1406 b, 1406 c, and 1406 d thatare determined based on the split shape mode information of the squarefirst coding unit 1400 may be determined based on the length of a longside thereof. For example, because the length of a side of the squarefirst coding unit 1400 equals the length of a long side of thenon-square second coding units 1402 a and 1402 b, and 1404 a and 1404 b,the first coding unit 1400 and the non-square second coding units 1402 aand 1402 b, and 1404 a and 1404 b may have the same depth, e.g., D.However, when the image decoding apparatus 100 splits the first codingunit 1400 into the four square second coding units 1406 a, 1406 b, 1406c, and 1406 d based on the split shape mode information, because thelength of a side of the square second coding units 1406 a, 1406 b, 1406c, and 1406 d is ½ times the length of a side of the first coding unit1400, a depth of the second coding units 1406 a, 1406 b, 1406 c, and1406 d may be D+1 which is deeper than the depth D of the first codingunit 1400 by 1.

According to an embodiment, the image decoding apparatus 100 maydetermine a plurality of second coding units 1412 a and 1412 b, and 1414a, 1414 b, and 1414 c by splitting a first coding unit 1410, a height ofwhich is longer than its width, in a horizontal direction based on thesplit shape mode information. According to an embodiment, the imagedecoding apparatus 100 may determine a plurality of second coding units1422 a and 1422 b, and 1424 a, 1424 b, and 1424 c by splitting a firstcoding unit 1420, a width of which is longer than its height, in avertical direction based on the split shape mode information.

According to an embodiment, a depth of the second coding units 1412 aand 1412 b, and 1414 a, 1414 b, and 1414 c, or 1422 a and 1422 b, and1424 a, 1424 b, and 1424 c, which are determined based on the splitshape mode information of the non-square first coding unit 1410 or 1420,may be determined based on the length of a long side thereof. Forexample, because the length of a side of the square second coding units1412 a and 1412 b is ½ times the length of a long side of the firstcoding unit 1410 having a non-square shape, a height of which is longerthan its width, a depth of the square second coding units 1412 a and1412 b is D+1 which is deeper than the depth D of the non-square firstcoding unit 1410 by 1.

Furthermore, the image decoding apparatus 100 may split the non-squarefirst coding unit 1410 into an odd number of second coding units 1414 a,1414 b, and 1414 c based on the split shape mode information. The oddnumber of second coding units 1414 a, 1414 b, and 1414 c may include thenon-square second coding units 1414 a and 1414 c and the square secondcoding unit 1414 b. In this case, because the length of a long side ofthe non-square second coding units 1414 a and 1414 c and the length of aside of the square second coding unit 1414 b are ½ times the length of along side of the first coding unit 1410, a depth of the second codingunits 1414 a, 1414 b, and 1414 c may be D+1 which is deeper than thedepth D of the non-square first coding unit 1410 by 1. The imagedecoding apparatus 100 may determine depths of coding units split fromthe first coding unit 1420 having a non-square shape, a width of whichis longer than its height, by using the aforementioned method ofdetermining depths of coding units split from the first coding unit1410.

According to an embodiment, the image decoding apparatus 100 maydetermine PIDs for identifying split coding units, based on a size ratiobetween the coding units when an odd number of split coding units do nothave equal sizes. Referring to FIG. 14 , a coding unit 1414 b of acenter location among an odd number of split coding units 1414 a, 1414b, and 1414 c may have a width being equal to that of the other codingunits 1414 a and 1414 c and a height being twice that of the othercoding units 1414 a and 1414 c. That is, in this case, the coding unit1414 b at the center location may include two of the other coding unit1414 a or 1414 c. Therefore, when a PID of the coding unit 1414 b at thecenter location is 1 based on a scan order, a PID of the coding unit1414 c located next to the coding unit 1414 b may be increased by 2 andthus may be 3. That is, discontinuity in PID values may be present.According to an embodiment, the image decoding apparatus 100 maydetermine whether an odd number of split coding units do not have equalsizes, based on whether discontinuity is present in PIDs for identifyingthe split coding units.

According to an embodiment, the image decoding apparatus 100 maydetermine whether to use a particular splitting method, based on PIDvalues for identifying a plurality of coding units determined bysplitting a current coding unit. Referring to FIG. 14 , the imagedecoding apparatus 100 may determine an even number of coding units 1412a and 1412 b or an odd number of coding units 1414 a, 1414 b, and 1414 cby splitting the first coding unit 1410 having a rectangular shape, aheight of which is longer than its width. The image decoding apparatus100 may use PIDs indicating respective coding units so as to identifythe respective coding units. According to an embodiment, the PID may beobtained from a sample at a preset location of each coding unit (e.g.,an upper left sample).

According to an embodiment, the image decoding apparatus 100 maydetermine a coding unit at a preset location from among the split codingunits, by using the PIDs for distinguishing the coding units. Accordingto an embodiment, when the split shape mode information of the firstcoding unit 1410 having a rectangular shape, a height of which is longerthan its width, indicates to split a coding unit into three codingunits, the image decoding apparatus 100 may split the first coding unit1410 into three coding units 1414 a, 1414 b, and 1414 c. The imagedecoding apparatus 100 may assign a PID to each of the three codingunits 1414 a, 1414 b, and 1414 c. The image decoding apparatus 100 maycompare PIDs of an odd number of split coding units so as to determine acoding unit at a center location from among the coding units. The imagedecoding apparatus 100 may determine the coding unit 1414 b having a PIDcorresponding to a middle value among the PIDs of the coding units, asthe coding unit at the center location from among the coding unitsdetermined by splitting the first coding unit 1410. According to anembodiment, the image decoding apparatus 100 may determine PIDs fordistinguishing split coding units, based on a size ratio between thecoding units when the split coding units do not have equal sizes.Referring to FIG. 14 , the coding unit 1414 b generated by splitting thefirst coding unit 1410 may have a width being equal to that of the othercoding units 1414 a and 1414 c and a height being twice that of theother coding units 1414 a and 1414 c. In this case, when the PID of thecoding unit 1414 b at the center location is 1, the PID of the codingunit 1414 c located next to the coding unit 1414 b may be increased by 2and thus may be 3. When the PID is not uniformly increased as describedabove, the image decoding apparatus 100 may determine that a coding unitis split into a plurality of coding units including a coding unit havinga size different from that of the other coding units. According to anembodiment, when the split shape mode information indicates to split acoding unit into an odd number of coding units, the image decodingapparatus 100 may split a current coding unit in such a manner that acoding unit of a preset location among an odd number of coding units(e.g., a coding unit of a centre location) has a size different fromthat of the other coding units. In this case, the image decodingapparatus 100 may determine the coding unit of the centre location,which has a different size, by using PIDs of the coding units. However,the PIDs and the size or location of the coding unit of the presetlocation are not limited to the aforementioned examples, and variousPIDs and various locations and sizes of coding units may be used.

According to an embodiment, the image decoding apparatus 100 may use apreset data unit where a coding unit starts to be recursively split.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

According to an embodiment, a preset data unit may be defined as a dataunit where a coding unit starts to be recursively split by using atleast one of block shape information and split shape mode information.That is, the preset data unit may correspond to a coding unit of anuppermost depth, which is used to determine a plurality of coding unitssplit from a current picture. In the following descriptions, forconvenience of explanation, the preset data unit is referred to as areference data unit.

According to an embodiment, the reference data unit may have a presetsize and a preset shape. According to an embodiment, the reference dataunit may include M×N samples. Herein, M and N may be equal to eachother, and may be integers expressed as powers of 2. That is, thereference data unit may have a square or non-square shape, and then maybe split into an integer number of coding units.

According to an embodiment, the image decoding apparatus 100 may splitthe current picture into a plurality of reference data units. Accordingto an embodiment, the image decoding apparatus 100 may split theplurality of reference data units, which are split from the currentpicture, by using the split shape mode information of each referencedata unit. The operation of splitting the reference data unit maycorrespond to a splitting operation using a quadtree structure.

According to an embodiment, the image decoding apparatus 100 maypreviously determine the minimum size allowed for the reference dataunits included in the current picture. Accordingly, the image decodingapparatus 100 may determine various reference data units having sizesequal to or greater than the minimum size, and may determine one or morecoding units by using the block shape information and the split shapemode information with reference to the determined reference data unit.

Referring to FIG. 15 , the image decoding apparatus 100 may use a squarereference coding unit 1500 or a non-square reference coding unit 1502.According to an embodiment, the shape and size of reference coding unitsmay be determined based on various data units that may include one ormore reference coding units (e.g., sequences, pictures, slices, slicesegments, tiles, tile groups, largest coding units, or the like).

According to an embodiment, the receiver (not shown) of the imagedecoding apparatus 100 may obtain, from a bitstream, at least one ofreference coding unit shape information and reference coding unit sizeinformation with respect to each of the various data units. An operationof splitting the square reference coding unit 1500 into one or morecoding units has been described above in relation to the operation ofsplitting the current coding unit 300 of FIG. 3 , and an operation ofsplitting the non-square reference coding unit 1502 into one or morecoding units has been described above in relation to the operation ofsplitting the current coding unit 400 or 450 of FIG. 4 . Thus, detaileddescriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 may use aPID for identifying the size and shape of reference coding units, todetermine the size and shape of reference coding units according to somedata units previously determined based on a preset condition. That is,the receiver (not shown) may obtain, from the bitstream, only the PIDfor identifying the size and shape of reference coding units withrespect to each slice, each slice segment, each tile, each tile group,or each largest coding unit which is a data unit satisfying a presetcondition (e.g., a data unit having a size equal to or smaller than aslice) among the various data units (e.g., sequences, pictures, slices,slice segments, tiles, tile groups, largest coding units, or the like).The image decoding apparatus 100 may determine the size and shape ofreference data units with respect to each data unit, which satisfies thepreset condition, by using the PID. When the reference coding unit shapeinformation and the reference coding unit size information are obtainedand used from the bitstream according to each data unit having arelatively small size, efficiency of using the bitstream may not behigh, and therefore, only the PID may be obtained and used instead ofdirectly obtaining the reference coding unit shape information and thereference coding unit size information. In this case, at least one ofthe size and shape of reference coding units corresponding to the PIDfor identifying the size and shape of reference coding units may bepreviously determined. That is, the image decoding apparatus 100 maydetermine at least one of the size and shape of reference coding unitsincluded in a data unit serving as a unit for obtaining the PID, byselecting the previously determined at least one of the size and shapeof reference coding units based on the PID.

According to an embodiment, the image decoding apparatus 100 may use oneor more reference coding units included in a largest coding unit. Thatis, a largest coding unit split from an image may include one or morereference coding units, and coding units may be determined byrecursively splitting each reference coding unit. According to anembodiment, at least one of a width and height of the largest codingunit may be integer times at least one of the width and height of thereference coding units. According to an embodiment, the size ofreference coding units may be obtained by splitting the largest codingunit n times based on a quadtree structure. That is, the image decodingapparatus 100 may determine the reference coding units by splitting thelargest coding unit n times based on a quadtree structure, and may splitthe reference coding unit based on at least one of the block shapeinformation and the split shape mode information according to variousembodiments.

FIG. 16 illustrates a processing block serving as a criterion fordetermining a determination order of reference coding units included ina picture 1600, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more processing blocks split from a picture. Theprocessing block is a data unit including one or more reference codingunits split from a picture, and the one or more reference coding unitsincluded in the processing block may be determined according to aparticular order. That is, a determination order of one or morereference coding units determined in each of processing blocks maycorrespond to one of various types of orders for determining referencecoding units, and may vary depending on the processing block. Thedetermination order of reference coding units, which is determined withrespect to each processing block, may be one of various orders, e.g.,raster scan order, Z-scan, N-scan, up-right diagonal scan, horizontalscan, and vertical scan, but is not limited to the aforementioned scanorders.

According to an embodiment, the image decoding apparatus 100 may obtainprocessing block size information and may determine the size of one ormore processing blocks included in the picture. The image decodingapparatus 100 may obtain the processing block size information from abitstream and may determine the size of one or more processing blocksincluded in the picture. The size of processing blocks may be a presetsize of data units, which is indicated by the processing block sizeinformation.

According to an embodiment, the receiver (not shown) of the imagedecoding apparatus 100 may obtain the processing block size informationfrom the bitstream according to each particular data unit. For example,the processing block size information may be obtained from the bitstreamin a data unit such as an image, sequence, picture, slice, slicesegment, or the like. That is, the receiver (not shown) may obtain theprocessing block size information from the bitstream according to eachof the various data units, and the image decoding apparatus 100 maydetermine the size of one or more processing blocks, which are splitfrom the picture, by using the obtained processing block sizeinformation. The size of the processing blocks may be integer times thatof the reference coding units.

According to an embodiment, the image decoding apparatus 100 maydetermine the size of processing blocks 1602 and 1612 included in thepicture 1600. For example, the image decoding apparatus 100 maydetermine the size of processing blocks based on the processing blocksize information obtained from the bitstream. Referring to FIG. 16 ,according to an embodiment, the image decoding apparatus 100 maydetermine a width of the processing blocks 1602 and 1612 to be fourtimes the width of the reference coding units, and may determine aheight of the processing blocks 1602 and 1612 to be four times theheight of the reference coding units. The image decoding apparatus 100may determine a determination order of one or more reference codingunits in one or more processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine the processing blocks 1602 and 1612, which are included in thepicture 1600, based on the size of processing blocks, and may determinea determination order of one or more reference coding units in theprocessing blocks 1602 and 1612. According to an embodiment,determination of reference coding units may include determination of thesize of the reference coding units.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, determination order information of one or morereference coding units included in one or more processing blocks, andmay determine a determination order with respect to one or morereference coding units based on the obtained determination orderinformation. The determination order information may be defined as anorder or direction for determining the reference coding units in theprocessing block. That is, the determination order of reference codingunits may be independently determined with respect to each processingblock.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, the determination order information of referencecoding units according to each particular data unit. For example, thereceiver (not shown) may obtain the determination order information ofreference coding units from the bitstream according to each data unitsuch as an image, sequence, picture, slice, slice segment, tile, tilegroup, or processing block. Because the determination order informationof reference coding units indicates an order for determining referencecoding units in a processing block, the determination order informationmay be obtained with respect to each particular data unit including aninteger number of processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more reference coding units based on the determineddetermination order.

According to an embodiment, the receiver (not shown) may obtain thedetermination order information of reference coding units from thebitstream as information related to the processing blocks 1602 and 1612,and the image decoding apparatus 100 may determine a determination orderof one or more reference coding units included in the processing blocks1602 and 1612 and may determine one or more reference coding units,which are included in the picture 1600, based on the determinationorder. Referring to FIG. 16 , the image decoding apparatus 100 maydetermine determination orders 1604 and 1614 of one or more referencecoding units in the processing blocks 1602 and 1612, respectively. Forexample, when the determination order information of reference codingunits is obtained with respect to each processing block, different typesof the determination order information of reference coding units may beobtained for the processing blocks 1602 and 1612. When the determinationorder 1604 of reference coding units in the processing block 1602 is araster scan order, reference coding units included in the processingblock 1602 may be determined according to a raster scan order. On thecontrary, when the determination order 1614 of reference coding units inthe other processing block 1612 is a backward raster scan order,reference coding units included in the processing block 1612 may bedetermined according to the backward raster scan order.

According to an embodiment, the image decoding apparatus 100 may decodethe determined one or more reference coding units. The image decodingapparatus 100 may decode an image, based on the reference coding unitsdetermined as described above. A method of decoding the reference codingunits may include various image decoding methods.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, block shape information indicating the shape of acurrent coding unit or split shape mode information indicating asplitting method of the current coding unit, and may use the obtainedinformation. The block shape information or the split shape modeinformation may be included in the bitstream related to various dataunits. For example, the image decoding apparatus 100 may use the blockshape information or the split shape mode information which is includedin a sequence parameter set, a picture parameter set, a video parameterset, a slice header, a slice segment header, a tile header, or a tilegroup header. Furthermore, the image decoding apparatus 100 may obtain,from the bitstream, a syntax element corresponding to the block shapeinformation or the split shape mode information according to eachlargest coding unit, each reference coding unit, or each processingblock, and may use the obtained syntax element.

With reference of FIGS. 17 to 20 , an image encoding apparatus and animage decoding apparatus, and an image encoding method and an imagedecoding method for encoding or decoding an image based on various-shapecoding units according to various embodiments will be described.

FIGS. 17 and 18 are diagrams for describing a method by which splittingto chroma blocks whose size is equal to or smaller than a preset size isnot allowed according to a splitting tree type, according to variousembodiments.

FIGS. 17A and 17B are diagrams for describing a method by whichsplitting to chroma blocks whose size is equal to or smaller than apreset size is not allowed when a splitting tree type indicates a singletree, according to various embodiments.

FIG. 17A is a diagram for describing a method by which splitting of achroma block whose size is equal to or smaller than a preset size is notallowed when a splitting tree type indicates a single tree, according toan embodiment.

When the splitting tree type indicates the single tree, a tree structureof coding units of a luma image and a tree structure of coding units ofa chroma image may be determined based on one tree structure of codingunits.

Referring to FIG. 17A, when the splitting tree type indicates the singletree, the image decoding apparatus 100 may binary split a luma block1705 and a corresponding chroma block 1710 in a vertical direction. Theimage decoding apparatus 100 may determine an allowable minimum size ofa luma block to be 4×4, and because a size of a block 1715 to begenerated due to binary splitting in the vertical direction is greaterthan the allowable minimum size of the luma block, the image decodingapparatus 100 may binary split the luma block 1705 in the verticaldirection.

The image decoding apparatus 100 may determine an allowable minimum sizeof a chroma block to be 4×4, and because a size of a block to begenerated due to binary splitting in a vertical direction is smallerthan the allowable minimum size of the chroma block, the image decodingapparatus 100 may determine to not split the chroma block 1710.

The image decoding apparatus 100 may binary split the luma block 1715and the corresponding chroma block 1710 in a horizontal direction. Theimage decoding apparatus 100 may determine an allowable minimum size ofa luma block to be 4×4, and because a size of a block 1720 to begenerated due to binary splitting in the horizontal direction is equalto the allowable minimum size of the luma block, the image decodingapparatus 100 may binary split the luma block 1715 in the horizontaldirection.

The image decoding apparatus 100 may determine an allowable minimum sizeof a chroma block to be 4×4, and because a size of a block to begenerated due to binary splitting in a horizontal direction is smallerthan the allowable minimum size of the chroma block, the image decodingapparatus 100 may determine to not split the chroma block 1710 any more.

FIG. 17B is a diagram for describing a method by which splitting tochroma blocks whose size is equal to or smaller than a preset size isnot allowed when a splitting tree type indicates a single tree,according to an embodiment.

FIG. 17B is a diagram for describing a method by which splitting tochroma blocks whose size is equal to or smaller than a preset size isnot allowed when a splitting tree type indicates a single tree,according to another embodiment.

Referring to FIG. 17B, when the splitting tree type indicates the singletree, the image decoding apparatus 100 may tri split a luma block 1755and a corresponding chroma block 1760 in a vertical direction. The imagedecoding apparatus 100 may determine an allowable minimum area of a lumablock to be 16, and because an area of a block 1765 to be generated dueto tri splitting in the vertical direction is equal to or greater thanthe allowable minimum area of the luma block, the image decodingapparatus 100 may tri split the luma block 1755 in the verticaldirection.

The image decoding apparatus 100 may determine an allowable minimum areaof a chroma block to be 16, and because an area of a block to begenerated due to tri splitting in a vertical direction is smaller thanthe allowable minimum area of the chroma block, the image decodingapparatus 100 may determine to not split the chroma block 1760.

FIG. 18 is a diagram for describing a method by which splitting of achroma block whose size is equal to or smaller than a preset size is notallowed when a splitting tree type indicates a dual tree, according toan embodiment.

When the splitting tree type indicates the dual tree, a tree structureof coding units of a luma image and a tree structure of coding units ofa chroma image may be separately determined.

Referring to FIG. 18 , the image decoding apparatus 100 may determine anallowable minimum size of a chroma block to be 4×4, and because a sizeof blocks to be generated by splitting chroma blocks 1800, 1810, 1820,and 1825 according to a particular split type is smaller than 4×4 thatis the allowable minimum size of the chroma block, the image decodingapparatus 100 may determine to not split a chroma block 1800 accordingto the particular split type.

When a split type of the chroma block 1800 indicates quad split, a sizeof a block to be generated by quad splitting the chroma block 1800 is2×2 smaller than 4×4 that is the allowable minimum size, and thus, theimage decoding apparatus 100 may determine to not split the chroma block1800 according to quad split. In this regard, as a condition based onthe size of the chroma block 1800, the image decoding apparatus 100 maydetermine whether the size of the block to be generated due to splittingis smaller than 4×4 that is the allowable minimum size. For example, theimage decoding apparatus 100 may determine whether a height or a widthof the chroma block 1800 is equal to or smaller than 4, and in responseto a result of the determination, the image decoding apparatus 100 maydetermine that the size of the block to be generated due to splitting issmaller than 4×4 that is the allowable minimum size.

When a split type of the chroma block 1810 indicates binary split, asize of a block to be generated by binary splitting the chroma block1810 is 4×2 or 2×4 which is smaller than 4×4 that is the allowableminimum size, and thus, the image decoding apparatus 100 may determineto not split the chroma block 1810 according to binary split. In thisregard, as a condition based on an area of the chroma block 1810, theimage decoding apparatus 100 may determine whether the size of the blockto be generated due to splitting is smaller than 4×4 that is theallowable minimum size. For example, the image decoding apparatus 100may determine whether the area of the chroma block 1810 is equal to orsmaller than 16, and in response to a result of the determination, theimage decoding apparatus 100 may determine that the size of the block tobe generated due to splitting is smaller than 4×4 that is the allowableminimum size.

When a split type of the chroma blocks 1820 and 1825 indicates trisplit, a size of blocks to be generated by tri splitting the chromablocks 1820 and 1825 is 4×2 or 2×4 which is smaller than 4×4 that is theallowable minimum size, and thus, the image decoding apparatus 100 maydetermine to not split chroma blocks 1820 and 1825 according to trisplit.

In this regard, as a condition based on an area of the chroma blocks1820 and 1825, the image decoding apparatus 100 may determine whetherthe size of the block to be generated due to splitting is smaller than4×4 that is the allowable minimum size. For example, the image decodingapparatus 100 may determine whether the area of the chroma blocks 1820and 1825 is equal to or smaller than 32, and in response to a result ofthe determination, the image decoding apparatus 100 may determine thatthe size of the block to be generated due to splitting is smaller than4×4 that is the allowable minimum size.

The image decoding apparatus 100 may determine a coding unit of a chromablock to be always equal to or greater than an allowable minimum size,thereby improving a throughput in decoding of the chroma block.

FIGS. 19 and 20 are diagrams for describing a method of splitting ablock at a boundary of a picture, according to various embodiments.

FIG. 19 is a diagram for describing a method of splitting a block, whichis located at a boundary of a picture, by using a split shape mode basedon a direction of the boundary, according to an embodiment.

The image decoding apparatus 100 may hierarchically quad split the blockby recursively performing quad splitting. Here, a range of a size of ablock to be generated due to quad splitting may be determined. The imagedecoding apparatus 100 may hierarchically quad split a block byrecursively performing quad splitting within a range of a size of ablock to be generated due to quad splitting.

The image decoding apparatus 100 may recursively perform binarysplitting or tri splitting on the block generated due to hierarchicalquad splitting. In this regard, a split depth of binary splitting or trisplitting may be predetermined. The image decoding apparatus 100 mayrecursively perform binary splitting or tri splitting on the block basedon the predetermined split depth of binary splitting or tri splitting,the block being generated due to hierarchical quad splitting.

Referring to FIG. 19 , when a current block 1900 is located at a pictureboundary 1905, the image decoding apparatus 100 may not obtain splitshape mode information from a bitstream and may split the current block1900 according to a split shape mode allowed with respect to the currentblock 1900. For example, when an allowable split type of a split shapemode of a current block is tri split or binary split, the image decodingapparatus 100 may binary split (or tri split) the current block 1900. Inthis regard, a split direction may be determined to be a horizontaldirection, based on a direction of the picture boundary 1905 of thecurrent block 1900.

When the allowable split type of the split shape mode of the currentblock is not tri split nor binary split, the image decoding apparatus100 may quad split the current block 1900.

The image decoding apparatus 100 may recursively split the current block1900 until a block generated due to splitting is not located at thepicture boundary 1905.

FIGS. 20A and 20B are diagrams for describing a method of splitting ablock at a picture boundary according to whether a minimum size of ablock is obtainable when the block at the picture boundary is binarysplit by applying an allowed binary split depth thereto, according to anembodiment.

Referring to FIG. 20A, in a case where a size of a current block 2000 is128×128, an allowable split type of the current block 2000 is binarysplit, and an allowable split depth of the current block 2000 is 3, whenthe current block 2000 is located at an image boundary 2005 of a currentpicture, the image decoding apparatus 100 may perform binary splittingbased on a first split boundary 2010, may perform binary splitting basedon a second split boundary 2015, and may perform binary splitting basedon a third split boundary 2020. Because binary splitting is performed asmuch as a binary split depth, the image decoding apparatus 100 cannotperform binary splitting any more. Therefore, a size of a block 2025inside the image boundary 2005, the block 2025 being determined as acoding unit, may be 16×128. However, because the size of the block 2025determined as a coding unit is not small, when the block 2025 includesvarious motion information and pixel value information, decodingefficiency deteriorates.

Referring to FIG. 20B, in a case where a size of a current block 2030 is128×128, an allowable split type of the current block 2030 is binarysplit, and an allowable split depth of the current block 2030 is 3, whenthe current block 2030 is located at an image boundary 2035 of a currentpicture, the image decoding apparatus 100 may perform binary splittingwhen a size of a block to be generated due to recursive binary splitfrom the current block 2030, in consideration of a size of the currentblock 2030 and an allowable split depth of binary split for the currentblock 2030, is equal to or smaller than a minimum block size (e.g.,4×4), and may perform quad splitting when a size of the block generateddue to recursive binary split from the current block 2030, inconsideration of the allowable split depth of binary split, is greaterthan the minimum block size.

Because the size of the block generated due to recursive binary splitfrom the current block 2030, in consideration of the allowable splitdepth of binary split, is greater than the minimum block size, the imagedecoding apparatus 100 may perform quad splitting on the current block2030, based on a first split boundary 2040.

Because a size of a block generated due to recursive binary split from acurrent block 2045, in consideration of a maximum allowable split depthof binary split, is greater than the minimum block size, the imagedecoding apparatus 100 may perform quad splitting on the current block2040, based on a second split boundary 2050.

Because a size of a block generated due to recursive binary split from acurrent block 2055, in consideration of the maximum allowable splitdepth of binary split, is equal to or smaller than the minimum blocksize, the image decoding apparatus 100 may perform binary splitting onthe current block 2055, based on a third split boundary 2060.

A size of a block 2065 inside the image boundary 2035, the block 2065being generated by performing binary splitting on the current block 2055based on the third split boundary 2060, is 16×32, and the image decodingapparatus 100 may additionally perform binary splitting on the block2065. Therefore, unlike FIG. 20A, a size of a block determined as acoding unit may be small, and decoding efficiency may be relativelyincreased.

When the image decoding apparatus 100 determines a size of the currentblock 2000 or 2030 to be 128×128, determines an allowable split type ofthe current block 2000 or 2030 to be binary split, and determines anallowable split depth of the current block 2000 or 2030 to be 3, amethod of splitting the current block 2000 or 2030 at a picture boundaryis described above with reference to FIGS. 20A and 20B, but thedisclosure is not limited thereto, and a current block located at apicture boundary may be split according to pseudocode.

[Pseudocode] bottom_boundary // indication of whether current block   // is bottom boundary of picture (0 when    // located at boundary 0,1 when not    // located) right_boundary // indication of whethercurrent block is   // right boundary of picture (0 when   // located atboundary 0, 1 when not   // located) max_bt_size // maximum block sizeallowing binary-tree  // (and triple-tree) min_bt_size // minimum blocksize bt_depth  // allowed binary-tree (and triple-tree) depth wGth  //width of current block height  // height of current block abs(v)  //indication of absolute value of v log2(v) // value of log where basenumber of v is 2    // (part for checking whether binary-tree isallowed)    // = width > max bt size || height > max bt size ||    //(part for checking whether minimum block size is    // obtainable whenallowed binary-tree is applied)    // abs(log2(width) − log2(min btsize)) > max bt depth ||    // abs(log2(height) − log2(min bt size)) >max bt size  if (!bottom_boundary || !right_boundary) && flag)     //(here abs( ) is omittable)   split by using quad-tree // (user-setparticular size    // may be used, instead of    // min_bt_size)  elseif (!bottom_boundary)   split by using binary-tree in horizontaldirection  else if (!right_boundary)   split by using binary-tree invertical direction  else   explicit determination of split mode

For example, in a case where the image decoding apparatus 100 thatfollows pseudocode above recursively performs splitting based on anallowed split depth according to binary split with respect to a greatervalue of a height or a width of a current block, when a correspondingside becomes a particular size (or smaller) (here, the particular sizemay be a minimum block size, or a size that is set by a user), the imagedecoding apparatus 100 may recursively split (split based on a binarytree) the current block according to binary split. Except for theaforementioned case, the image decoding apparatus 100 may split thecurrent block according to quad split. In detail, in a case where anallowed binary split depth (bt_depth) is 3, only when a greater valuefrom among a height and a width of the current block is equal to orsmaller than a minimum size(min_bt_size)×2×2×2 (i.e., a minimum size×8),the current block may be recursively split according to binary split.

With reference to FIGS. 20A and 20B, a method by which the imagedecoding apparatus 100 performs binary splitting or quad splitting, inconsideration of a binary split depth, is described, but the disclosureis not limited thereto, and thus, one of ordinary skill in the art caneasily understand that the image decoding apparatus 100 may binarysplit, tri split, or quad split a current block based on a binary (andtri) split depth, in a similar manner.

The disclosure has been particularly shown and described with referenceto embodiments thereof. In this regard, it will be understood by one ofordinary skill in the art that various changes in form and details maybe made therein without departing from the scope of the disclosure.Therefore, the embodiments should be considered in a descriptive senseonly and not for purposes of limitation. The scope of the disclosure isdefined not by the detailed descriptions of the disclosure but by thefollowing claims, and all differences within the scope will be construedas being included in the disclosure.

Meanwhile, the aforedescribed embodiments of the disclosure can bewritten as a program executable on a computer, and can be implemented ingeneral-use digital computers that execute the program by using acomputer-readable recording medium. Examples of the computer-readablerecording medium include magnetic storage media (e.g., ROM, floppydisks, hard disks, etc.), optical recording media (e.g., CD-ROMs, orDVDs), or the like.

1. An image decoding method, comprising: obtaining one or more lumacoding units based on at least one of a split direction and a split typeof a luma block; decoding a luma image based on the obtained one or moreluma coding units; when an area of a chroma block is smaller than orequal to an area predetermined according to tri split type of the chromablock, determining not to allow splitting of the chroma block accordingto the tri split type and obtaining one or more chroma coding unitsaccording to a split type except for the tri split type; and decoding achroma image based on the obtained one or more chroma coding unitsaccording to the split type.
 2. The image decoding method of claim 1,wherein the area predetermined according to the tri split type is
 32. 3.An image decoding apparatus, comprising: at least one processorconfigured to: obtain one or more luma coding units based on at leastone of a split direction and a split type of a luma block; decode a lumaimage based on the obtained one or more luma coding units; when an areaof a chroma block is smaller than or equal to an area predeterminedaccording to tri split type of the chroma block, determine not to allowsplitting of the chroma block according to the tri split type and obtainone or more chroma coding units according to a split type except for thetri split type; and decode a chroma image based on the obtained one ormore chroma coding units according to the split type.
 4. An imageencoding method, comprising: determining one or more luma coding unitsbased on at least one of a split direction and a split type of a lumablock; encoding a luma image based on the obtained one or more lumacoding units; when an area of a chroma block is smaller than or equal toan area predetermined according to tri split type of the chroma block,determining not to allow splitting of the chroma block according to thetri split type and determining one or more chroma coding units accordingto a split type except for the tri split type; and encoding a chromaimage based on the obtained one or more chroma coding units according tothe split type.
 5. A non-transitory computer-readable recording mediumhaving recorded thereon a program for performing the image decodingmethod of claim 1.